apply: fix access to an uninitialized mode variable, found by valgrind

When 'tpatch' was initialized successfully, st_mode was already taken
from the previous diff.  We should not try to override it with data
from an lstat() that was never called.

This is a companion patch to 7a07841(git-apply: handle a patch that
touches the same path more than once better).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -2445,7 +2445,7 @@ static int check_preimage(struct patch *patch, struct cache_entry **ce, struct s
 		return error("%s: %s", old_name, strerror(errno));
 	}
 
-	if (!cached)
+	if (!cached && !tpatch)
 		st_mode = ce_mode_from_stat(*ce, st->st_mode);
 
 	if (patch->is_new < 0)