Fixed race condition in Source:play (thanks Boolsheet)

src/modules/audio/openal/Pool.cpp

@@ -118,11 +118,11 @@ int Pool::getMaxSources() const
 
 bool Pool::play(Source *source, ALuint &out)
 {
-	bool ok;
-	out = 0;
-
 	thread::Lock lock(mutex);
 
+	bool ok = true;
+	out = 0;
+
 	bool alreadyPlaying = findSource(source, out);
 
 	if (!alreadyPlaying)