avcodec/h264_slice: Check input SPS in ff_h264_update_thread_context()

Fixes: crash
Fixes: check_pkt.mp4

Found-by: Rafael Dutra <rafael.dutra@cispa.de>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h264_slice.c

@@ -304,9 +304,8 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
     if (dst == src)
         return 0;
 
-    // We can't fail if SPS isn't set at it breaks current skip_frame code
-    //if (!h1->ps.sps)
-    //    return AVERROR_INVALIDDATA;
+    if (inited && !h1->ps.sps)
+        return AVERROR_INVALIDDATA;
 
     if (inited &&
         (h->width                 != h1->width                 ||