Fix potential OOB when checking for trailing spaces

If `path_len` is zero, we must not access `path`, let alone try to
subtract `-1` from it.

Since `path` and `path_len` are supposed to come from a `zend_string`,
this is not a security issue.

Closes GH-17471.

Author: cmb69

NEWS

@@ -11,6 +11,7 @@ PHP                                                                        NEWS
     inherited final). (ilutov)
   . Fixed NULL arithmetic during system program execution on Windows. (cmb,
     nielsdos)
+  . Fixed potential OOB when checking for trailing spaces on Windows. (cmb)
 
 - Enchant:
   . Fix crashes in enchant when passing null bytes. (nielsdos)

win32/winutil.c

@@ -56,7 +56,7 @@ PHP_WINUTIL_API void php_win32_error_msg_free(char *msg)
 
 int php_win32_check_trailing_space(const char * path, const size_t path_len)
 {/*{{{*/
-	if (path_len > MAXPATHLEN - 1) {
+	if (path_len == 0 || path_len > MAXPATHLEN - 1) {
 		return 1;
 	}
 	if (path) {