tool_doswin: increase allowable length of path sanitizer

tool_doswin: increase allowable length of path sanitizer

- Use 32767-1 instead of PATH_MAX-1 (260-1) as the maximum allowable
  length of a path in Windows.

Prior to this change the path sanitizer in Windows used 32767-1 as the
maximum length only for paths that had the "\\" prefix like
"\\?\longpath". Since then we added some workarounds to open longer
paths without "\\?\" prefix by normalizing the path and adding that
prefix, and the sanitizer is called before the prefix is added.

Bug: https://github.com/curl/curl/issues/20044
Reported-by: Viktor Szakats
Closes https://github.com/curl/curl/pull/20046