avcodec/h264_slice: Fix overflow in recovery_frame computation

Fixes: signed integer overflow: 15 + 2147483646 cannot be represented in type 'int'
Fixes: 8381/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-6225533137321984

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 8c20ea8ee0)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h264_sei.c

@@ -261,10 +261,16 @@ static int decode_unregistered_user_data(H264SEIUnregistered *h, GetBitContext *
     return 0;
 }
 
-static int decode_recovery_point(H264SEIRecoveryPoint *h, GetBitContext *gb)
+static int decode_recovery_point(H264SEIRecoveryPoint *h, GetBitContext *gb, void *logctx)
 {
-    h->recovery_frame_cnt = get_ue_golomb_long(gb);
+    unsigned recovery_frame_cnt = get_ue_golomb_long(gb);
 
+    if (recovery_frame_cnt >= (1<<MAX_LOG2_MAX_FRAME_NUM)) {
+        av_log(logctx, AV_LOG_ERROR, "recovery_frame_cnt %u is out of range\n", recovery_frame_cnt);
+        return AVERROR_INVALIDDATA;
+    }
+
+    h->recovery_frame_cnt = recovery_frame_cnt;
     /* 1b exact_match_flag,
      * 1b broken_link_flag,
      * 2b changing_slice_group_idc */
@@ -429,7 +435,7 @@ int ff_h264_sei_decode(H264SEIContext *h, GetBitContext *gb,
             ret = decode_unregistered_user_data(&h->unregistered, gb, logctx, size);
             break;
         case H264_SEI_TYPE_RECOVERY_POINT:
-            ret = decode_recovery_point(&h->recovery_point, gb);
+            ret = decode_recovery_point(&h->recovery_point, gb, logctx);
             break;
         case H264_SEI_TYPE_BUFFERING_PERIOD:
             ret = decode_buffering_period(&h->buffering_period, gb, ps, logctx);