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.