Heap buffer out of bounds write in start_decoder in stb_vorbis

stb_vorbis is a single file MIT licensed library for processing ogg vorbis files. A crafted file may trigger out of bounds write in f->vendor[len] = (char)'\0';. The root cause is that if len read in start_decoder is a negative number and setup_malloc successfully allocates memory in that case, but memory write is done with a negative index len. Similarly if len is INT_MAX the integer overflow len+1 happens in f->vendor = (char*)setup_malloc(f, sizeof(char) * (len+1)); and f->comment_list[i] = (char*)setup_malloc(f, sizeof(char) * (len+1));. This issue may lead to code execution.