unregister as window manager before restarting (fixes a race condition)

src/manage.c

@@ -64,6 +64,10 @@ void restore_geometry(void) {
                                 con->rect.x, con->rect.y);
         }
 
+    /* Strictly speaking, this line doesn’t really belong here, but since we
+     * are syncing, let’s un-register as a window manager first */
+    xcb_change_window_attributes(conn, root, XCB_CW_EVENT_MASK, (uint32_t[]){ XCB_EVENT_MASK_SUBSTRUCTURE_REDIRECT });
+
     /* Make sure our changes reach the X server, we restart/exit now */
     xcb_aux_sync(conn);
 }