rootston: Keep focus unchanged when non-focusable element clicked

Before this change, a view would lose focus after clicking something that's not keyboard-interactive. This would lead to edge cases with layer-shell windows like input methods, which are pointer-only-interactive, but are not intended to change the state of any focus.

rootston/cursor.c

@@ -273,7 +273,9 @@ static void roots_cursor_press_button(struct roots_cursor *cursor,
 			}
 			break;
 		case WLR_BUTTON_PRESSED:
-			roots_seat_set_focus(seat, view);
+			if (view) {
+				roots_seat_set_focus(seat, view);
+			}
 			if (surface && wlr_surface_is_layer_surface(surface)) {
 				struct wlr_layer_surface *layer =
 					wlr_layer_surface_from_wlr_surface(surface);