fixup! mingw: remove 248-char limit when creating directories

Actually, this commit was totally misguided. The path length limit for
non-long paths (at least before Windows 10 build 1067 with long paths
opted in) *is* 248, and we still want to convert to Root Local Device
Path if that limit is reached.

I misread the intention of the code when I made that patch to "remove
the 248-char limit", thinking that there was a hard limit to 248
characters even in the long path case, which was incorrect.

Simply revert that commit and be done.

This fixes #1084

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -496,7 +496,9 @@ int mingw_mkdir(const char *path, int mode)
 {
 	int ret;
 	wchar_t wpath[MAX_LONG_PATH];
-	if (xutftowcs_long_path(wpath, path) < 0)
+	/* CreateDirectoryW path limit is 248 (MAX_PATH - 8.3 file name) */
+	if (xutftowcs_path_ex(wpath, path, MAX_LONG_PATH, -1, 248,
+			core_long_paths) < 0)
 		return -1;
 
 	ret = _wmkdir(wpath);