Fixed OpenAL errors when removing looping sounds

The sounds didn't save their source id in the Sound.Loop method, so they couldn't stop the playback upon removal which caused errors when unbinding and deleting the (still playing) sound buffer

Subsurface/Source/Sounds/Sound.cs

@@ -198,8 +198,8 @@ namespace Barotrauma
                 return sourceIndex;
             }
 
-            return SoundManager.Loop(this, sourceIndex, relativePos/100.0f, volume);
-
+            alSourceId = SoundManager.Loop(this, sourceIndex, relativePos / 100.0f, volume);
+            return alSourceId;
         }
 
         public bool IsPlaying