orm: fix code generation for an option time.Time field (#20031)

vlib/orm/orm_option_time_test.v

@@ -0,0 +1,54 @@
+import db.sqlite
+import time
+
+@[table: 'foos']
+struct Foo {
+	id         int        @[primary; sql: serial]
+	name       string
+	created_at time.Time  @[default: 'CURRENT_TIME']
+	updated_at ?string    @[sql_type: 'TIMESTAMP']
+	deleted_at ?time.Time
+	children   []Child    @[fkey: 'parent_id']
+}
+
+struct Child {
+	id        int    @[primary; sql: serial]
+	parent_id int
+	name      string
+}
+
+fn test_main() {
+	mut db := sqlite.connect(':memory:') or { panic(err) }
+	defer {
+		db.close() or { panic(err) }
+	}
+
+	sql db {
+		create table Foo
+	}!
+	foo := Foo{
+		name: 'abc'
+		created_at: time.now()
+		// updated_at defaults to none
+		// deleted_at defaults to none
+		children: [
+			Child{
+				name: 'abc'
+			},
+			Child{
+				name: 'def'
+			},
+		]
+	}
+
+	sql db {
+		insert foo into Foo
+	}!
+
+	data := sql db {
+		select from Foo
+	}![0]
+	assert data.id == 1
+	assert data.updated_at == none
+	assert data.deleted_at == none
+}