orm: fix codegen for option fk (fix #23383) (#23400)

vlib/orm/orm_option_subselect_test.v

@@ -0,0 +1,49 @@
+import db.sqlite
+
+fn test_main() {
+	db := sqlite.connect(':memory:')!
+
+	sql db {
+		create table Commit
+		create table Measurement
+	}!
+
+	c := Commit{
+		commit_hash: 'hash'
+	}
+	sql db {
+		insert c into Commit
+	}!
+
+	c2 := sql db {
+		select from Commit
+	}!
+	assert c2[0].v_self_default == none
+
+	c3 := Commit{
+		commit_hash:    'hash1'
+		v_self_default: Measurement{
+			id: 123
+		}
+	}
+	sql db {
+		insert c3 into Commit
+	}!
+
+	c4 := sql db {
+		select from Commit
+	}!
+	assert c4[0].v_self_default == none
+	assert c4[1].v_self_default != none
+}
+
+@[table: 'commits']
+struct Commit {
+	commit_hash    string @[primary]
+	v_self_default ?Measurement
+}
+
+@[table: 'measurements']
+struct Measurement {
+	id int @[primary; serial]
+}