Reset item model when reference is reset (Fixes #1628)

This caused crashes when the window was resized after the reference no longer exists (e.g. when a savegame is loaded)
Fix compile error for OPENMW_USE_FFMPEG=0
Fix initializing CharacterController with fists or spell equipped
Cancel queued view mode switch when switching view mode (Fixes #1618)
Merge remote-tracking branch 'scrawl/openmw-31' into openmw-31
updated changelog