patch 9.2.1219: Vim9: reading past garray when inheriting interfaces

Problem:  Vim9: when a class implements interfaces and extends a class
          that implements interfaces, checking whether an interface of
          the parent class is already present reads past the garray
          structure instead of using its items.
Solution: Use the items of the garray (Yegappan Lakshmanan).

fixes:  #21569
closes: #21508

Assisted-by: Claude
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_vim9_interface.vim

@@ -1514,6 +1514,36 @@ def Test_interface_method_returns_own_class()
   v9.CheckSourceFailure(lines, 'E1383: Method "Copy": type mismatch, expected func(): object<I> but got func(): object<Other>', 11)
 enddef
 
+" Test for a class inheriting an interface from the parent class, while it
+" implements several interfaces itself
+def Test_implements_with_parent_interface()
+  var lines =<< trim END
+    vim9script
+    interface I1
+    endinterface
+    interface I2
+    endinterface
+    interface I3
+    endinterface
+    interface I4
+    endinterface
+    interface I5
+      def F(): number
+    endinterface
+    class A implements I5
+      def F(): number
+        return 5
+      enddef
+    endclass
+    class B extends A implements I1, I2, I3, I4
+    endclass
+    var i5: I5 = B.new()
+    assert_equal(5, i5.F())
+    assert_true(instanceof(B.new(), I1, I4, I5))
+  END
+  v9.CheckSourceSuccess(lines)
+enddef
+
 " Test interface garbage collection {{{1
 func Test_interface_garbagecollect()
   let lines =<< trim END

src/version.c

@@ -743,6 +743,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1219,
 /**/
     1218,
 /**/

src/vim9class.c

@@ -928,7 +928,7 @@ is_interface_class_present(garray_T *intf_classes_gap, class_T *ifcl)
 {
     for (int j = 0; j < intf_classes_gap->ga_len; j++)
     {
-	if (((class_T **)intf_classes_gap)[j] == ifcl)
+	if (((class_T **)intf_classes_gap->ga_data)[j] == ifcl)
 	    return TRUE;
     }