patch 9.0.1942: Vim9: execution stack invalidated with null object

Problem:  Vim9: execution stack invalidated with null object
Solution: Check for a null object before adjusting the execution stack

closes: #13186

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/version.c b/src/version.c
index 168c10c..e48c564 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1942,
+/**/
     1941,
 /**/
     1940,
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 02a37e8..0700eb7 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -535,6 +535,15 @@
     // 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 (IS_OBJECT_METHOD(ufunc) && !IS_CONSTRUCTOR_METHOD(ufunc)
+	    && obj->v_type == VAR_OBJECT && obj->vval.v_object == NULL)
+    {
+	// If this is not a 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;
@@ -601,15 +610,6 @@
     // 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;
     }