fix from https://gitlab.xiph.org/xiph/vorbis-tools/-/merge_requests/7

 diff --git a/oggenc/platform.c b/oggenc/platform.c
 index 6d9f4ef..b66e47a 100644
 --- a/oggenc/platform.c
 +++ b/oggenc/platform.c
 @@ -136,18 +136,22 @@ int create_directories(char *fn, int isutf8)
  {
      char *end, *start;
      struct stat statbuf;
 -    char *segment = malloc(strlen(fn)+1);
 +    const size_t fn_len = strlen(fn);
 +    char *segment = malloc(fn_len+1);
  #ifdef _WIN32
      wchar_t seg[MAX_PATH+1];
  #endif
  
      start = fn;
  #ifdef _WIN32
 -    if(strlen(fn) >= 3 && isalpha(fn[0]) && fn[1]==':')
 +    // Strip drive prefix
 +    if(fn_len >= 3 && isalpha(fn[0]) && fn[1]==':') {
 + 
          start = start+2;
  #endif
  
 -    while((end = strpbrk(start+1, PATH_SEPS)) != NULL)
 +    // Loop through path segments, creating directories if necessary
 +    while((end = strpbrk(start + strspn(start, PATH_SEPS), PATH_SEPS)) != NULL)
      {
          int rv;
          memcpy(segment, fn, end-fn);