Prevent the currently displayed video frame from changing if the video is paused

If you'd seek while the video was paused, you'd see the next frame of the video.

src/modules/video/theora/TheoraVideoStream.cpp

@@ -293,6 +293,9 @@ bool TheoraVideoStream::swapBuffers()
 	if (demuxer.isEos())
 		return false;
 
+	if (!frameSync->isPlaying())
+		return false;
+
 	love::thread::Lock l(bufferMutex);
 	if (!frameReady)
 		return false;