Do not register unexisting section

[nickvergessen]

{
  "reqId": "Iuw8V2rje6ggUm3Enm3A",
  "level": 1,
  "time": "2019-02-27T12:16:10+01:00",
  "remoteAddr": "127.0.0.1",
  "user": "admin",
  "app": "no app in context",
  "method": "GET",
  "url": "\/index.php\/settings\/admin\/talk",
  "message": {
    "Exception": "OCP\\AppFramework\\QueryException",
    "Message": "Could not resolve OCA\\Theming\\Settings\\Section! Class OCA\\Theming\\Settings\\Section does not exist",
    "Code": 0,
    "Trace": [
      {
        "file": "\/lib\/private\/AppFramework\/Utility\/SimpleContainer.php",
        "line": 119,
        "function": "resolve",
        "class": "OC\\AppFramework\\Utility\\SimpleContainer",
        "type": "->",
        "args": [
          "OCA\\Theming\\Settings\\Section"
        ]
      },
      {
        "file": "\/lib\/private\/ServerContainer.php",
        "line": 136,
        "function": "query",
        "class": "OC\\AppFramework\\Utility\\SimpleContainer",
        "type": "->",
        "args": [
          "OCA\\Theming\\Settings\\Section"
        ]
      },
      {
        "file": "\/lib\/private\/Settings\/Manager.php",
        "line": 104,
        "function": "query",
        "class": "OC\\ServerContainer",
        "type": "->",
        "args": [
          "OCA\\Theming\\Settings\\Section"
        ]
      },
      {
        "file": "\/lib\/private\/Settings\/Manager.php",
        "line": 200,
        "function": "getSections",
        "class": "OC\\Settings\\Manager",
        "type": "->",
        "args": [
          "admin"
        ]
      },
      {
        "file": "\/settings\/Controller\/CommonSettingsTrait.php",
        "line": 100,
        "function": "getAdminSections",
        "class": "OC\\Settings\\Manager",
        "type": "->",
        "args": [
          
        ]
      },
      {
        "file": "\/settings\/Controller\/CommonSettingsTrait.php",
        "line": 51,
        "function": "formatAdminSections",
        "class": "OC\\Settings\\Controller\\AdminSettingsController",
        "type": "->",
        "args": [
          "admin",
          "talk"
        ]
      },
      {
        "file": "\/settings\/Controller\/CommonSettingsTrait.php",
        "line": 125,
        "function": "getNavigationParameters",
        "class": "OC\\Settings\\Controller\\AdminSettingsController",
        "type": "->",
        "args": [
          "admin",
          "talk"
        ]
      },
      {
        "file": "\/settings\/Controller\/AdminSettingsController.php",
        "line": 65,
        "function": "getIndexResponse",
        "class": "OC\\Settings\\Controller\\AdminSettingsController",
        "type": "->",
        "args": [
          "admin",
          "talk"
        ]
      },
      {
        "file": "\/lib\/private\/AppFramework\/Http\/Dispatcher.php",
        "line": 166,
        "function": "index",
        "class": "OC\\Settings\\Controller\\AdminSettingsController",
        "type": "->",
        "args": [
          "talk"
        ]
      },
      {
        "file": "\/lib\/private\/AppFramework\/Http\/Dispatcher.php",
        "line": 99,
        "function": "executeController",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\Settings\\Controller\\AdminSettingsController"
          },
          "index"
        ]
      },
      {
        "file": "\/lib\/private\/AppFramework\/App.php",
        "line": 118,
        "function": "dispatch",
        "class": "OC\\AppFramework\\Http\\Dispatcher",
        "type": "->",
        "args": [
          {
            "__class__": "OC\\Settings\\Controller\\AdminSettingsController"
          },
          "index"
        ]
      },
      {
        "file": "\/lib\/private\/AppFramework\/Routing\/RouteActionHandler.php",
        "line": 47,
        "function": "main",
        "class": "OC\\AppFramework\\App",
        "type": "::",
        "args": [
          "OC\\Settings\\Controller\\AdminSettingsController",
          "index",
          {
            "__class__": "OC\\AppFramework\\DependencyInjection\\DIContainer"
          },
          {
            "section": "talk",
            "_route": "settings.AdminSettings.index"
          }
        ]
      },
      {
        "function": "__invoke",
        "class": "OC\\AppFramework\\Routing\\RouteActionHandler",
        "type": "->",
        "args": [
          {
            "section": "talk",
            "_route": "settings.AdminSettings.index"
          }
        ]
      },
      {
        "file": "\/lib\/private\/Route\/Router.php",
        "line": 297,
        "function": "call_user_func",
        "args": [
          {
            "__class__": "OC\\AppFramework\\Routing\\RouteActionHandler"
          },
          {
            "section": "talk",
            "_route": "settings.AdminSettings.index"
          }
        ]
      },
      {
        "file": "\/lib\/base.php",
        "line": 987,
        "function": "match",
        "class": "OC\\Route\\Router",
        "type": "->",
        "args": [
          "\/settings\/admin\/talk"
        ]
      },
      {
        "file": "\/index.php",
        "line": 42,
        "function": "handleRequest",
        "class": "OC",
        "type": "::",
        "args": [
          
        ]
      }
    ],
    "File": "\/lib\/private\/AppFramework\/Utility\/SimpleContainer.php",
    "Line": 104,
    "CustomMessage": "--"
  },
  "userAgent": "Mozilla\/5.0 (X11; Ubuntu; Linux x86_64; rv:65.0) Gecko\/20100101 Firefox\/65.0",
  "version": "16.0.0.1"
}

[MorrisJobke]

Breaking change: 2cd3fd3 from #13097 - so no need to backport.