wildmatch: change behavior of "foo**bar" in WM_PATHNAME mode

In WM_PATHNAME mode (or FNM_PATHNAME), '*' does not match '/' and '**'
can but only in three patterns:

- '**/' matches zero or more leading directories
- '/**/' matches zero or more directories in between
- '/**' matches zero or more trailing directories/files

When '**' is present but not in one of these patterns, the current
behavior is consider the pattern invalid and stop matching. In other
words, 'foo**bar' never matches anything, whatever you throw at it.

This behavior is arguably a bit confusing partly because we can't
really tell the user their pattern is invalid so that they can fix
it. So instead, tolerate it and make '**' act like two regular '*'s
(which is essentially the same as a single asterisk). This behavior
seems more predictable.

Noticed-by: dana <dana@dana.is>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/wildmatch.c b/wildmatch.c
index d074c1b..9e9e2a2 100644
--- a/wildmatch.c
+++ b/wildmatch.c
@@ -104,8 +104,8 @@ static int dowild(const uchar *p, const uchar *text, unsigned int flags)
 					    dowild(p + 1, text, flags) == WM_MATCH)
 						return WM_MATCH;
 					match_slash = 1;
-				} else
-					return WM_ABORT_MALFORMED;
+				} else /* WM_PATHNAME is set */
+					match_slash = 0;
 			} else
 				/* without WM_PATHNAME, '*' == '**' */
 				match_slash = flags & WM_PATHNAME ? 0 : 1;