CINE: Fix lockup in Scene 5 when "operate Girl" underwater.

Traced with gdb to sound.cpp:792 i.e. _fadeOutTimer infinite loop.

This bug was introduced by the addition of the MT-32 output driver for
Future Wars and associated mutex changes.
The _fadeOutTimer increment is done by the timer callback occuring
during the load method call, but this was excluded by the mutex.

Fixed by moving the mutex in the load method.

engines/cine/sound.cpp

@@ -785,14 +785,15 @@ PCSoundFxPlayer::~PCSoundFxPlayer() {
 
 bool PCSoundFxPlayer::load(const char *song) {
 	debug(9, "PCSoundFxPlayer::load('%s')", song);
-	Common::StackLock lock(_mutex);
 
 	/* stop (w/ fade out) the previous song */
 	while (_fadeOutCounter != 0 && _fadeOutCounter < 100) {
 		g_system->delayMillis(50);
 	}
 	_fadeOutCounter = 0;
 
+	Common::StackLock lock(_mutex);
+
 	stop();
 
 	_sfxData = readBundleSoundFile(song);