window.c: Fix SIGSEGV in pointer_handle_motion

Move null pointer check and assignments before first window dereference.

clients/window.c

@@ -2904,6 +2904,12 @@ pointer_handle_motion(void *data, struct wl_pointer *pointer,
 	float sx = wl_fixed_to_double(sx_w);
 	float sy = wl_fixed_to_double(sy_w);
 
+	input->sx = sx;
+	input->sy = sy;
+
+	if (!window)
+		return;
+
 	/* when making the window smaller - e.g. after a unmaximise we might
 	 * still have a pending motion event that the compositor has picked
 	 * based on the old surface dimensions
@@ -2912,12 +2918,6 @@ pointer_handle_motion(void *data, struct wl_pointer *pointer,
 	    sy > window->main_surface->allocation.height)
 		return;
 
-	input->sx = sx;
-	input->sy = sy;
-
-	if (!window)
-		return;
-
 	if (!(input->grab && input->grab_button)) {
 		widget = window_find_widget(window, sx, sy);
 		input_set_focus_widget(input, widget, sx, sy);