fix populate-filespec

I hand munged the original patch when committing 1510fea7, and
screwed up the conversion.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

diff.c

@@ -1223,7 +1223,7 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int
 	 * objects however would tend to be slower as they need
 	 * to be individually opened and inflated.
 	 */
-	if (FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(sha1, NULL))
+	if (!FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(sha1, NULL))
 		return 0;
 
 	len = strlen(name);