Fix code that breaks with VC (terrible compiler)

VC2013 still does not properly support placement of variables anywhere
in the scope.  It's a garbage compiler, always will be a garbage
compiler.

libobs/util/threading.h

@@ -40,10 +40,10 @@ extern "C" {
 /* this may seem strange, but you can't use it unless it's an initializer */
 static inline void pthread_mutex_init_value(pthread_mutex_t *mutex)
 {
+	pthread_mutex_t init_val = PTHREAD_MUTEX_INITIALIZER;
 	if (!mutex)
 		return;
 
-	pthread_mutex_t init_val = PTHREAD_MUTEX_INITIALIZER;
 	*mutex = init_val;
 }