avcodec/cbs_av1: Check leb128 values read

"It is a requirement of bitstream conformance that the value returned from the leb128 parsing process is less than or equal
to (1 << 32) - 1."

Fixes: assertion failure
Fixes: 19293/clusterfuzz-testcase-minimized-ffmpeg_BSF_TRACE_HEADERS_fuzzer-5749508361420800

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cbs_av1.c

@@ -170,6 +170,9 @@ static int cbs_av1_read_leb128(CodedBitstreamContext *ctx, GetBitContext *gbc,
             break;
     }
 
+    if (value > UINT32_MAX)
+        return AVERROR_INVALIDDATA;
+
     if (ctx->trace_enable)
         ff_cbs_trace_syntax_element(ctx, position, name, NULL, "", value);