diff-lib: use worktree mode in diffs from i-t-a entries

When creating "new file" diffs against i-t-a index entries, diff-lib
erroneously used the mode of the cache entry rather than the mode of the
file in the worktree. This changes run_diff_files() to correctly use the
mode of the worktree file in this case.

Signed-off-by: Raymond E. Pasco <ray@ameretat.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -219,7 +219,8 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 				continue;
 			} else if (revs->diffopt.ita_invisible_in_index &&
 				   ce_intent_to_add(ce)) {
-				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
+				newmode = ce_mode_from_stat(ce, st.st_mode);
+				diff_addremove(&revs->diffopt, '+', newmode,
 					       &null_oid, 0, ce->name, 0);
 				continue;
 			}