h264: support frame parameter changes during frame-mt

Fixes CVE-2012-2782.

libavcodec/h264.h

@@ -448,6 +448,8 @@ typedef struct H264Context {
     int nal_length_size;  ///< Number of bytes used for nal length (1, 2 or 4)
     int got_first;        ///< this flag is != 0 if we've parsed a frame
 
+    int context_reinitialized;
+
     SPS *sps_buffers[MAX_SPS_COUNT];
     PPS *pps_buffers[MAX_PPS_COUNT];