Fix: Crash when moving GP frame so that it replaces the one before it
This crash only occurred in a particular file, when onion skinning was enabled. For some reason, the fact that this function was clearing the layer's actframe (when the frame being deleted wasn't currently active) was causing problems. I'm guessing that the GP draw engine code currently assumes that gpl->actframe will always be set/valid?
Moved all the datablock-twiddling version patching magic to the "after_liblink" version patching function. Apparently the problem was that many of the old pointers had not been fixed up at that point, causing problems if relying on accessing their contents.