ffmpeg: Stack-buffer-overflow in ff_htmlmarkup_to_ass

Detailed report: https://clusterfuzz-external.appspot.com/testcase?key=6380176053108736 Target: ffmpeg Fuzzer: libFuzzerffmpegSUBTITLEAVCODECIDSUBRIPfuzzer Fuzzer binary: ffmpegSUBTITLEAVCODECIDSUBRIPfuzzer Job Type: libfuzzerasanffmpeg Platform Id: linux Crash Type: Stack-buffer-overflow READ 1...