Change for lock since parent member of MenuCacheItem isn't protected by reference.
Change for lock since parent member of MenuCacheItem isn't protected by reference.

The parent in MenuCacheItem isn't protected by reference therefore we
should establish a lock before test for removal the item, not before
actual removal. Otherwise another thread may increase reference on the
parent which we think is already free.

lxde/menu-cache,lxde/menu-cache