Attempt to free an uninitialized memory pointer in vorbis_deinit in stb_vorbis

stb_vorbis is a single file MIT licensed library for processing ogg vorbis files. A crafted file may trigger memory allocation failure in start_decoder. In that case the function returns early, but some of the pointers in f->comment_list are left initialized and later setup_free is called on these pointers in vorbis_deinit. This issue may lead to code execution.