continue to focus monitor under mouse cursor

dwl.c

@@ -550,6 +550,9 @@ motionabsolute(struct wl_listener *listener, void *data)
 void
 motionnotify(uint32_t time)
 {
+	/* Update selmon (even while dragging a window) */
+	selmon = xytomon(cursor->x, cursor->y);
+
 	/* If we are currently grabbing the mouse, handle and return */
 	if (cursor_mode == CurMove) {
 		/* Move the grabbed client to the new position. */