fix(FDLGEN): Allow empty method files (refs #4518)

Treat empty method file as if no method file had been specified in the first
place.

Also:
- Removed unused instantiation of new Layout("FDL/Layout/Class.Method.xml")
test(FDLGEN): Add test for FDLGEN method generation (refs #4518)
Merge pull request #1103 from eguaj/3.2-A4518

fix(FDLGEN): Allow empty method files (closes #4518)