merge-recursive: do not die on a conflicting submodule

We cannot represent the 3-way conflicted state in the work tree
for these entries, but it is normal not to have commit objects
for them in our repository.  Just update the index and the life
will be good.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -520,8 +520,12 @@ static void update_file_flags(struct merge_options *o,
 		unsigned long size;
 
 		if (S_ISGITLINK(mode))
-			die("cannot read object %s '%s': It is a submodule!",
-			    sha1_to_hex(sha), path);
+			/*
+			 * We may later decide to recursively descend into
+			 * the submodule directory and update its index
+			 * and/or work tree, but we do not do that now.
+			 */
+			goto update_index;
 
 		buf = read_sha1_file(sha, &type, &size);
 		if (!buf)