video mixer: fix bad frame re-use

Some of internal stats of a frame could be re-used by ffmpeg,
but the frame doesn't have been reset for that.
This endings into potential multiple crashes.

This patch forces frame reset before re-use.

Issue: #81689
Change-Id: I9fa1c7e0d7a19d4abc8e44cb8978fa9379d51abf

src/media/video/video_mixer.cpp

@@ -109,6 +109,8 @@ VideoMixer::update(Observable<std::shared_ptr<VideoFrame>>* ob,
         if (x->source == ob) {
             if (!x->update_frame)
                 x->update_frame.reset(new VideoFrame);
+            else
+                x->update_frame->reset();
             *x->update_frame = *frame_p;
             x->atomic_swap_render(x->update_frame);
             return;