Fix crash on (unset) cast in constant property initializer

Author: arshidkv12

Zend/tests/ast/gh21072.phpt

@@ -11,5 +11,5 @@ try {
     echo $e->getMessage();
 }
 ?>
---EXPECT--
-Invalid cast in constant expression
+--EXPECTF--
+Fatal error: The (unset) cast is no longer supported in %s on line %d

Zend/zend_compile.c

@@ -12565,6 +12565,10 @@ static void zend_eval_const_expr(zend_ast **ast_ptr) /* {{{ */
 			return;
 		case ZEND_AST_CAST:
 			zend_eval_const_expr(&ast->child[0]);
+			if (ast->attr == IS_NULL) {
+				zend_error(E_COMPILE_ERROR, "The (unset) cast is no longer supported");
+				break;
+			}
 			if (ast->child[0]->kind == ZEND_AST_ZVAL
 			 && zend_try_ct_eval_cast(&result, ast->attr, zend_ast_get_zval(ast->child[0]))) {
 				break;