h264: Make sure reinit failures mark the context as not initialized

(cherry picked from commit 3b69f245db)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>

Conflicts:
	libavcodec/h264_slice.c
(cherry picked from commit 964fef3f3c)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Conflicts:

	libavcodec/h264.c

libavcodec/h264.c

@@ -3389,7 +3389,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
          h->height != h->avctx->coded_height  ||
          must_reinit ||
          needs_reinit)) {
-
+        h->context_initialized = 0;
         if (h != h0) {
             av_log(h->avctx, AV_LOG_ERROR, "changing width/height on "
                    "slice %d\n", h0->current_slice + 1);