When running the program for the first time, no scene collections will
show up in the scene collection menu. This changes it to forcibly save
the first scene collection on the first run of the program, and then
re-enumerates the list to ensure it's listed.
This commit fixes a bug that would cause the frontend API function
obs_frontend_set_current_scene_collection to never be successful. Due
to the bug, the following null pointer check would always fail, so the
action would never be triggered.
Modification by Jim: Instead of fixing the typo that caused this to
occur, make it so both scene collection menus and profile menus both use
"file_name" consistently.
Closesjp9000/obs-studio#712
