clearing scene only if file open doesn't fail

Author: tatatupi

src/FlowScene.cpp

@@ -500,10 +500,6 @@ void
 FlowScene::
 load()
 {
-  clearScene();
-
-  //-------------
-
   QString fileName =
     QFileDialog::getOpenFileName(nullptr,
                                  tr("Open Flow Scene"),
@@ -518,6 +514,8 @@ load()
   if (!file.open(QIODevice::ReadOnly))
     return;
 
+  clearScene();
+
   QByteArray wholeFile = file.readAll();
 
   loadFromMemory(wholeFile);