Fix for MAGN-794: File tab not showing file name.

Two defects addressing this issue:
http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-794
http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-2184

The issue was caused by this change: https://github.com/DynamoDS/Dynamo/commit/c0b382eb637f2cf31b7421fd2240b43b6560e85a. I'm not entirely sure if that was intended.