graphicsmagick:coder_AVIF_fuzzer: Use-of-uninitialized-value in HeifContext::has_alpha

Project: http://hg.code.sf.net/p/graphicsmagick/code Detailed Report: https://oss-fuzz.com/testcase?key=4820668783329280 Project: graphicsmagick Fuzzing Engine: libFuzzer Fuzz Target: coderAVIFfuzzer Job Type: libfuzzermsangraphicsmagick Platform Id: linux Crash Type: Use-of-uninitialized-value...