patch 9.0.1932: Vim9: error when using null object constructor

Problem:  Vim9: error when using null object constructor
Solution: Check for a null object only when calling an object method

closes: #13154
closes: #13163

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/vim9execute.c b/src/vim9execute.c
index a53b1b3..2fc7f34 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -535,15 +535,6 @@
     // If this is an object method, the object is just before the arguments.
     typval_T	*obj = STACK_TV_BOT(0) - argcount - vararg_count - 1;
 
-    if (obj->v_type == VAR_OBJECT && obj->vval.v_object == NULL
-					&& !IS_CONSTRUCTOR_METHOD(ufunc))
-    {
-	// If this is not the constructor method, then a valid object is
-	// needed.
-	emsg(_(e_using_null_object));
-	return FAIL;
-    }
-
     // Check the argument types.
     if (check_ufunc_arg_types(ufunc, argcount, vararg_count, ectx) == FAIL)
 	return FAIL;
@@ -610,6 +601,15 @@
     // the first local variable.
     if (IS_OBJECT_METHOD(ufunc))
     {
+	if (obj->v_type == VAR_OBJECT && obj->vval.v_object == NULL
+					    && !IS_CONSTRUCTOR_METHOD(ufunc))
+	{
+	    // If this is not a constructor method, then a valid object is
+	    // needed.
+	    emsg(_(e_using_null_object));
+	    return FAIL;
+	}
+
 	*STACK_TV_VAR(0) = *obj;
 	obj->v_type = VAR_UNKNOWN;
     }