desktop-shell: Further consolidate move/resize grab checks

This moves the check for shsurf->grabbed into surface_move() and
surface_resize(), which are shared with the xwayland code.  This prevents
trying to resize or move an xwayland window with multiple pointers.

desktop-shell/shell.c

@@ -1556,7 +1556,8 @@ surface_move(struct shell_surface *shsurf, struct weston_seat *seat,
 	if (!shsurf)
 		return -1;
 
-	if (shsurf->state.fullscreen || shsurf->state.maximized)
+	if (shsurf->grabbed ||
+	    shsurf->state.fullscreen || shsurf->state.maximized)
 		return 0;
 
 	move = malloc(sizeof *move);
@@ -1583,9 +1584,6 @@ common_surface_move(struct wl_resource *resource,
 	struct shell_surface *shsurf = wl_resource_get_user_data(resource);
 	struct weston_surface *surface;
 
-	if (shsurf->grabbed)
-		return;
-
 	if (seat->pointer &&
 	    seat->pointer->focus &&
 	    seat->pointer->button_count > 0 &&
@@ -1746,7 +1744,8 @@ surface_resize(struct shell_surface *shsurf,
 {
 	struct weston_resize_grab *resize;
 
-	if (shsurf->state.fullscreen || shsurf->state.maximized)
+	if (shsurf->grabbed ||
+	    shsurf->state.fullscreen || shsurf->state.maximized)
 		return 0;
 
 	if (edges == 0 || edges > 15 ||
@@ -1777,12 +1776,6 @@ common_surface_resize(struct wl_resource *resource,
 	struct shell_surface *shsurf = wl_resource_get_user_data(resource);
 	struct weston_surface *surface;
 
-	if (shsurf->state.fullscreen)
-		return;
-
-	if (shsurf->grabbed)
-		return;
-
 	if (seat->pointer->button_count == 0 ||
 	    seat->pointer->grab_serial != serial ||
 	    seat->pointer->focus == NULL)