Release all grabs when unmanaging windows

When a window is unmapped, awesome stops tracking it, possibly
leaving stale grabs behind.  These grabs can be activated if the
window is mapped again without awesome’s knowledge.  This results
in a locked pointer until the grab window is destroyed.

Fix by releasing passive grabs before untracking a client window.

objects/client.c

@@ -3010,6 +3010,8 @@ client_unmanage(client_t *c, client_unmanage_t reason)
 
     if(reason != CLIENT_UNMANAGE_DESTROYED)
     {
+        xwindow_buttons_grab(c->window, &(button_array_t){ .len = 0 });
+        xwindow_grabkeys(c->window, &(key_array_t){ .len = 0 });
         area_t geometry = client_get_undecorated_geometry(c);
         xcb_unmap_window(globalconf.connection, c->window);
         xcb_reparent_window(globalconf.connection, c->window, globalconf.screen->root,