merge: setup opts later in checkout_fast_forward()

After we initialize the various fields in `opts` but before we actually
use them, we might return early. Move the initialization further down,
to immediately before we use `opts`.

This limits the scope of `opts` and will help a later commit fix a
memory leak without having to worry about those early returns.

This patch is best viewed using something like this (note the tab!):
--color-moved --anchored="	trees[nr_trees] = parse_tree_indirect"

Signed-off-by: Martin Ågren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Martin Ågren

merge.c

@@ -94,8 +94,24 @@ int checkout_fast_forward(const struct object_id *head,
 		return -1;
 
 	memset(&trees, 0, sizeof(trees));
-	memset(&opts, 0, sizeof(opts));
 	memset(&t, 0, sizeof(t));
+
+	trees[nr_trees] = parse_tree_indirect(head);
+	if (!trees[nr_trees++]) {
+		rollback_lock_file(&lock_file);
+		return -1;
+	}
+	trees[nr_trees] = parse_tree_indirect(remote);
+	if (!trees[nr_trees++]) {
+		rollback_lock_file(&lock_file);
+		return -1;
+	}
+	for (i = 0; i < nr_trees; i++) {
+		parse_tree(trees[i]);
+		init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
+	}
+
+	memset(&opts, 0, sizeof(opts));
 	if (overwrite_ignore) {
 		memset(&dir, 0, sizeof(dir));
 		dir.flags |= DIR_SHOW_IGNORED;
@@ -112,20 +128,6 @@ int checkout_fast_forward(const struct object_id *head,
 	opts.fn = twoway_merge;
 	setup_unpack_trees_porcelain(&opts, "merge");
 
-	trees[nr_trees] = parse_tree_indirect(head);
-	if (!trees[nr_trees++]) {
-		rollback_lock_file(&lock_file);
-		return -1;
-	}
-	trees[nr_trees] = parse_tree_indirect(remote);
-	if (!trees[nr_trees++]) {
-		rollback_lock_file(&lock_file);
-		return -1;
-	}
-	for (i = 0; i < nr_trees; i++) {
-		parse_tree(trees[i]);
-		init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
-	}
 	if (unpack_trees(nr_trees, t, &opts)) {
 		rollback_lock_file(&lock_file);
 		return -1;