Don't allow playing a sound/soundgen key more than once at the same time on the same object (Fixes #2689)

apps/openmw/mwmechanics/character.cpp

@@ -756,6 +756,7 @@ void CharacterController::handleTextKey(const std::string &groupname, const std:
     if(evt.compare(0, 7, "sound: ") == 0)
     {
         MWBase::SoundManager *sndMgr = MWBase::Environment::get().getSoundManager();
+        sndMgr->stopSound3D(mPtr, evt.substr(7));
         sndMgr->playSound3D(mPtr, evt.substr(7), 1.0f, 1.0f);
         return;
     }
@@ -796,7 +797,10 @@ void CharacterController::handleTextKey(const std::string &groupname, const std:
                                     MWBase::SoundManager::Play_NoPlayerLocal);
             }
             else
+            {
+                sndMgr->stopSound3D(mPtr, sound);
                 sndMgr->playSound3D(mPtr, sound, volume, pitch);
+            }
         }
         return;
     }