tui: newt: remove NULL checks after dereference

priv->start_buttons and priv->end_buttons are initialized at
construction and never changed and so the checks are not needed.

(cherry picked from commit 50ae9c936c)

clients/tui/newt/nmt-newt-button-box.c

@@ -262,13 +262,11 @@ nmt_newt_button_box_size_request (NmtNewtWidget *widget,
 	size_request_buttons (bbox, priv->start_buttons, width, height);
 	size_request_buttons (bbox, priv->end_buttons, width, height);
 
-	if (priv->start_buttons && priv->end_buttons) {
 	if (priv->orientation == NMT_NEWT_BUTTON_BOX_HORIZONTAL)
 		*width += 1;
 	else
 		*height += 1;
 }
-}
 
 static void
 nmt_newt_button_box_size_allocate (NmtNewtWidget *widget,