compat/fnmatch: fix off-by-one character class's length check

Character class "xdigit" is the only one that hits 6 character limit
defined by CHAR_CLASS_MAX_LENGTH. All other character classes are 5
character long and therefore never caught by this.

This should make xdigit tests in t3070 pass on Windows.
Reported-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

compat/fnmatch/fnmatch.c

@@ -345,7 +345,7 @@ internal_fnmatch (pattern, string, no_leading_period, flags)
 
 		    for (;;)
 		      {
-			if (c1 == CHAR_CLASS_MAX_LENGTH)
+			if (c1 > CHAR_CLASS_MAX_LENGTH)
 			  /* The name is too long and therefore the pattern
 			     is ill-formed.  */
 			  return FNM_NOMATCH;