Fix the private field crash for the Array object.

jerry-core/vm/opcodes.c

@@ -916,6 +916,11 @@ opfunc_private_method_or_accessor_add (ecma_object_t *class_object_p, /**< the f
 
     JERRY_ASSERT (prop_name_p->u.hash & ECMA_SYMBOL_FLAG_PRIVATE_INSTANCE_METHOD);
 
+    if (ecma_op_object_is_fast_array (this_obj_p))
+    {
+      ecma_fast_array_convert_to_normal (this_obj_p);
+    }
+
     prop_p = ecma_find_named_property (this_obj_p, prop_name_p);
     ecma_object_t *method_p = ecma_get_object_from_value (method);
 
@@ -1366,6 +1371,11 @@ opfunc_private_field_add (ecma_value_t base, /**< base object */
   ecma_string_t *prop_name_p = ecma_get_string_from_value (property);
   ecma_string_t *private_key_p = NULL;
 
+  if (ecma_op_object_is_fast_array (obj_p))
+  {
+      ecma_fast_array_convert_to_normal (obj_p);
+  }
+
   ecma_property_t *prop_p = opfunc_find_private_element (obj_p, prop_name_p, &private_key_p, false);
 
   if (prop_p != NULL)

tests/jerry/private_fields.js

@@ -327,3 +327,22 @@ class O {
 var var16 = new O();
 var16.b();
 assert(var16.c() == 12);
+
+// Private fields are accessible in Array object
+class C3 extends Array{
+  #a=1;
+  b(){
+    return this.#a;
+   }
+}
+var var17 = new C3();
+assert(var17.b()==1);
+
+class C4 extends Array{
+  #a(){return 1}; 
+  b(){
+    return this.#a();
+   }
+}
+var var18 = new C4();
+assert(var18.b()==1);