PlatformPlayer: Do not close the synthesizer on close().

This appears to be unnecessary, and it not only broke custom
soundfont support, but also made it so Orcs and Elves' effects
play shorter than intended.

src/org/recompile/mobile/PlatformPlayer.java

@@ -454,7 +454,7 @@ public void deallocate() { } // Prefetch does "nothing" in each internal player
 		public void close() 
 		{
 			midi.close();
-			synthesizer.close();
+			synthesizer = null;
 			midiSequence = null;
 			receiver = null;
 		}