LEAF 3288 address common logged errors

[aerinkayne]

Address some common errors logged in Dynatrace (frontend JS)

1. Prevent a ReferenceError in the LEAF Inbox that occurs if the quick view is displayed

2. Prevent a TypeError that can occur when the dialogController attempts to modify attributes of the cancel button.

3. Prevent a TypeError that could occur due to an incorrect indicators.conditions value.
   When the Conditions Editor was released, a brief issue caused form packets to be exported with indicator.conditions set to 'null' instead of null. This update handles this value for existing forms and prevents it from being set if a form packet that has the value is imported.

Impact / Testing

1. Inbox
   Open any form quick view. Dev Console Reference Error should no longer occur.

2. Potentially anywhere dialogController is used. This error can be re-produced by modifying a template that uses the dialog controller instance (For example, print_form) and misspelling the id passed for the cancel button. Confirm that the error no longer occurs.

3. Form Editor - Import Form, Request Editing and Preview areas
   Use Adminer to set an indicator's conditions to null (the string, not NULL from dropdown).
   -Confirm that no error occurs in the console on the form editing or print views.
   -Export the associated form, then re-import it. Confirm that the value for the imported form is NULL and not 'null'.