Fix skipped lazy init on primed SIMPLE_WRITE

Fixes GH-17998

Author: iluuu1994

Zend/tests/lazy_objects/gh17998.phpt

@@ -0,0 +1,31 @@
+--TEST--
+GH-17998: Skipped lazy init on primed SIMPLE_WRITE
+--FILE--
+<?php
+
+class C {
+    public $prop {
+        set => $value;
+    }
+}
+
+$nonLazy = new C;
+
+$lazy = (new ReflectionClass(C::class))->newLazyProxy(function () {
+    echo "init\n";
+    return new C;
+});
+
+function foo(C $c) {
+    $c->prop = 1;
+    var_dump($c->prop);
+}
+
+foo($nonLazy);
+foo($lazy);
+
+?>
+--EXPECT--
+int(1)
+init
+int(1)

Zend/zend_vm_def.h

@@ -2529,11 +2529,13 @@ ZEND_VM_C_LABEL(fast_assign_obj):
 				if (ZEND_IS_PROPERTY_HOOK_SIMPLE_WRITE(prop_offset)) {
 					zend_property_info *prop_info = CACHED_PTR_EX(cache_slot + 2);
 					property_val = OBJ_PROP(zobj, prop_info->offset);
-					if (ZEND_TYPE_IS_SET(prop_info->type)) {
-						value = zend_assign_to_typed_prop(prop_info, property_val, value, &garbage EXECUTE_DATA_CC);
-						ZEND_VM_C_GOTO(free_and_exit_assign_obj);
-					} else {
-						ZEND_VM_C_GOTO(fast_assign_obj);
+					if (Z_TYPE_P(property_val) != IS_UNDEF) {
+						if (ZEND_TYPE_IS_SET(prop_info->type)) {
+							value = zend_assign_to_typed_prop(prop_info, property_val, value, &garbage EXECUTE_DATA_CC);
+							ZEND_VM_C_GOTO(free_and_exit_assign_obj);
+						} else {
+							ZEND_VM_C_GOTO(fast_assign_obj);
+						}
 					}
 				}
 				/* Fall through to write_property for hooks. */