Out of bounds heap buffer write in stb_vorbis

stb_vorbis is a single file MIT licensed library for processing ogg vorbis files. A crafted file may trigger memory write past an allocated heap buffer in start_decoder. The root cause is a potential integer overflow in sizeof(char*) * (f->comment_list_length) which may make setup_malloc allocate less memory than required. Since there is another integer overflow an attacker may overflow it too to force setup_malloc to return 0 and make the exploit more reliable. This issue may lead to code execution.