checker: cleanup of is_sumtype_variant_infix()

lib/bait/checker/infix.bt

@@ -58,25 +58,21 @@ fun (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 
 // x is Variant
 fun (c Checker) is_sumtype_variant_infix(mut node ast.InfixExpr) ast.Type {
+	mut right := node.right as ast.Ident
+	if right.pkg == "" and c.pkg != 'main' and c.pkg != "builtin" {
+		right.pkg = c.pkg
+	}
+	node.right_type = c.table.get_idx(right.full_name())
+
 	// Smartcast variable
 	if node.left is ast.Ident {
-		mut right := node.right as ast.Ident
-		if right.pkg == "" and c.pkg != 'main' {
-			right.pkg = c.pkg
-		}
-		node.right_type = c.table.get_idx(right.full_name())
 		left := node.left as ast.Ident
 		c.scope.update_type(left.full_name(), node.right_type)
 		return ast.BOOL_TYPE
 	}
 
 	// Smartcast struct field
 	if node.left is ast.SelectorExpr {
-		mut right := node.right as ast.Ident
-		if right.pkg == "" and c.pkg != 'main' {
-			right.pkg = c.pkg
-		}
-		node.right_type = c.table.get_idx(right.full_name())
 		left := node.left as ast.SelectorExpr
 		name := (left.expr as ast.Ident).full_name() + '.' + left.field_name
 		c.scope.update_type(name, node.right_type)