edit-dialog: hide Delete button when creating a new event

Because we don't want to delete an event that is not created

src/gcal-edit-dialog.c

@@ -646,6 +646,7 @@ gcal_edit_dialog_set_event_is_new (GcalEditDialog *dialog,
 
   priv = gcal_edit_dialog_get_instance_private (dialog);
   priv->event_is_new = event_is_new;
+  gtk_widget_set_visible (GTK_WIDGET (priv->delete_button), !event_is_new);
 }
 
 void

src/gcal-window.c

@@ -713,6 +713,9 @@ event_activated (GcalView        *view,
     init_edit_dialog (GCAL_WINDOW (user_data));
 
   data = gcal_event_widget_get_data (event_widget);
+  gcal_edit_dialog_set_event_is_new (
+      GCAL_EDIT_DIALOG (priv->edit_dialog),
+      FALSE);
   gcal_edit_dialog_set_event_data (
       GCAL_EDIT_DIALOG (priv->edit_dialog),
       data);