Don't ignore custom formats in wxDataViewCtrl::EnableDropTarget()

Since the changes of 7129d2b11c (Accept multiple data formats via
drag-and-drop in wxDataViewCtrl, 2021-08-22) custom data formats were
simply ignored because CreateDataObject() helper didn't do anything for
them.

Fix this by simply continuing to handle them in the same way as before,
i.e. by creating a wxCustomDataObject for the specified format.

Closes #22112.

src/common/datavcmn.cpp

@@ -1735,6 +1735,7 @@ wxDataViewCtrlBase::CreateDataObject(const wxVector<wxDataFormat>& formats)
             case wxDF_ENHMETAFILE:
             case wxDF_LOCALE:
             case wxDF_PRIVATE:
+            default: // any other custom format
                 dataObject->Add(new wxCustomDataObject(formats[i]));
                 break;