Fixed SoundManager::stopSound when output is not initialized (bug #4600 probably)

apps/openmw/mwsound/soundmanagerimp.cpp

@@ -747,6 +747,9 @@ namespace MWSound
 
     void SoundManager::stopSound(const std::string& soundId)
     {
+        if(!mOutput->isInitialized())
+            return;
+
         Sound_Buffer *sfx = loadSound(Misc::StringUtils::lowerCase(soundId));
         if (!sfx) return;
 
@@ -755,6 +758,9 @@ namespace MWSound
 
     void SoundManager::stopSound3D(const MWWorld::ConstPtr &ptr, const std::string& soundId)
     {
+        if(!mOutput->isInitialized())
+            return;
+
         Sound_Buffer *sfx = loadSound(Misc::StringUtils::lowerCase(soundId));
         if (!sfx) return;