Fix THP shutdown crash

Cleanly shut down movie player threads on exit.

I'm not 100% fond of having to manually insert a call like this into the shutdown logic, but the other solution is shutting down all processes and that's likely to result in causing more crashes.

include/d/actor/d_a_movie_player.h

@@ -94,6 +94,12 @@ static void __THPAudioInitialize(THPAudioDecodeInfo* info, u8* ptr);
 #define THP_TEXTURE_SET_COUNT  3
 #endif
 
+#if TARGET_PC
+namespace dusk {
+    void MoviePlayerShutdown();
+}
+#endif
+
 struct daMP_THPPlayer {
     /* 0x000 */ DVDFileInfo fileInfo;
 	/* 0x03C */ THPHeader header;