Added null check to avoid NPE when throwing an exception for removing a queue file that doesn't exist.
Issue: MIRTH-2157
MIRTH-3033: Added a local declaration to the "i" variable used in the validate function so it doesn't cause any conflicts.
Fixed the filter pane so that moving a non-rule builder rule over a rule builder rule will not rename the former to the latter.

Fixed the transformer pane so that moving an external script or XSLT step over a mapper step will not rename the former to the latter.
Issue: MIRTH-2538