checker: check struct field reference type mismatch (#13575)

vlib/v/checker/struct.v

@@ -319,7 +319,7 @@ pub fn (mut c Checker) struct_init(mut node ast.StructInit) ast.Type {
 					}
 				} else {
 					if field_info.typ.is_ptr() && !expr_type.is_ptr() && !expr_type.is_pointer()
-						&& !expr_type.is_number() {
+						&& field.expr.str() != '0' {
 						c.error('reference field must be initialized with reference',
 							field.pos)
 					}

vlib/v/checker/tests/struct_field_reference_type_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_field_reference_type_err.vv:17:3: error: reference field must be initialized with reference
+   15 |
+   16 |     animal.duck = Duck{
+   17 |         age: animal.ageee
+      |         ~~~~~~~~~~~~~~~~~
+   18 |     }
+   19 |     dump(animal.duck.age)

vlib/v/checker/tests/struct_field_reference_type_err.vv

@@ -0,0 +1,20 @@
+struct Animal {
+mut:
+	ageee int
+	duck  Duck
+}
+
+struct Duck {
+	age &int
+}
+
+fn main() {
+	mut animal := Animal{
+		ageee: 20
+	}
+
+	animal.duck = Duck{
+		age: animal.ageee
+	}
+	dump(animal.duck.age)
+}