fix(math hook): undefined variable $operator error

[gitrequests]

Fix PHP warning: Undefined variable $operator in ERROR log. Because $operator variable is not defined in else statement.

[jolichter]

Hi, I get the same error by using the math hook:

(ERROR @ .../components/formit/src/FormIt/Request.php : 125) PHP warning: Undefined variable $operator
(ERROR @ .../components/formit/src/FormIt/Request.php : 131) PHP warning: Undefined variable $operator

The fix works, please use it in the next update.

Environment:

• MODX 3.0.2
• FormIt 5.0.1