Fix to handle longest lacing on empty arrays

It used to crash, it now doesn't execute the function

http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4566

@junmendoza @ke-yu PTAL

This needs cherry picking into 2015, and RC0.7.2_master, RC0.7.2_Revit2015 and folding into testing.

I'm not able to run the full test suite from where I am if you could give me a hand with that it would be much appreciated.