AVCodecDecoder: remove annoying assert.

According to Colin this is not supposed to happen, but it does. Since
the affected video otherwise decodes just fine, I think it is safe to
disable the assert and not annoy our users.

Fixes #11409.

src/add-ons/media/plugins/ffmpeg/AVCodecDecoder.cpp

@@ -1158,7 +1158,14 @@ AVCodecDecoder::_UpdateMediaHeaderForAudioFrame()
 status_t
 AVCodecDecoder::_DecodeNextVideoFrame()
 {
+#if 0
+	// Well, I heard this was not supposed to happen, but it does
+	// (for example with http://thud.us/videos/misc/xvid-samples/flyby-divx.avi
+	// see #11409). Since that video otherwise plays fine when removing the
+	// assert, I'm assuming we are being overcautious here and commenting it
+	// out.
 	assert(fTempPacket.size >= 0);
+#endif
 
 	while (true) {
 		status_t loadingChunkStatus