openal: Fix paused sounds not resuming from where they were paused (#1031)

panda/src/audiotraits/openalAudioSound.cxx

@@ -832,6 +832,8 @@ set_active(bool active) {
           // ...we're pausing a looping sound.
           _paused=true;
         }
+        // Store off the current time so we can resume from where we paused.
+        _start_time = get_time();
         stop();
       }
     }