reset: don't compute unstaged changes after reset when --quiet

When git reset is run with the --quiet flag, don't bother finding any
additional unstaged changes as they won't be output anyway.  This speeds up
the git reset command by avoiding having to lstat() every file looking for
changes that aren't going to be reported anyway.

The savings can be significant.  In a repo on Windows with 200K files
"git reset" drops from 7.16 seconds to 0.32 seconds for a savings of 96%.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/reset.c

@@ -376,7 +376,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			int flags = quiet ? REFRESH_QUIET : REFRESH_IN_PORCELAIN;
 			if (read_from_tree(&pathspec, &oid, intent_to_add))
 				return 1;
-			if (get_git_work_tree())
+			if (!quiet && get_git_work_tree())
 				refresh_index(&the_index, flags, NULL, NULL,
 					      _("Unstaged changes after reset:"));
 		} else {