setup.c: stop prefix_pathspec() from looping past the end of string

The code assumes that the string ends at either `)` or `,`, and does
not handle the case where strcspn() returns length due to end of
string.  So specifying ":(top" as pathspec will cause the loop to go
past the end of string.

Signed-off-by: Andrew Wong <andrew.kw.w@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

setup.c

@@ -199,10 +199,11 @@ static const char *prefix_pathspec(const char *prefix, int prefixlen, const char
 		     *copyfrom && *copyfrom != ')';
 		     copyfrom = nextat) {
 			size_t len = strcspn(copyfrom, ",)");
-			if (copyfrom[len] == ')')
-				nextat = copyfrom + len;
-			else
+			if (copyfrom[len] == ',')
 				nextat = copyfrom + len + 1;
+			else
+				/* handle ')' and '\0' */
+				nextat = copyfrom + len;
 			if (!len)
 				continue;
 			for (i = 0; i < ARRAY_SIZE(pathspec_magic); i++)