orm: fix code generated for fields of ?[]Type (#20032)

vlib/orm/orm_option_array_test.v

@@ -0,0 +1,45 @@
+import db.sqlite
+
+struct Member {
+	id       int      @[primary]
+	children ?[]Child @[fkey: parent_id]
+}
+
+struct Child {
+	id        int @[primary]
+	parent_id int
+}
+
+fn test_main() {
+	mut db := sqlite.connect(':memory:') or { panic(err) }
+	defer {
+		db.close() or { panic(err) }
+	}
+	sql db {
+		create table Member
+	} or { println(err) }
+	sql db {
+		create table Child
+	} or { println(err) }
+	new_member := Member{
+		id: 1
+		children: [Child{
+			id: 1
+			parent_id: 1
+		}, Child{
+			id: 2
+			parent_id: 1
+		}]
+	}
+	sql db {
+		insert new_member into Member
+	}!
+
+	rows := sql db {
+		select from Member
+	}!
+
+	assert rows[0].children?.len == 2
+	assert rows[0].children?[0].id == 1
+	assert rows[0].children?[1].id == 2
+}