PowerD: Prevent potential dependency loop in get*Capacity
PowerD: Prevent potential dependency loop in get*Capacity

Not currently happening in vanilla code, but, not entirely unlikely.
stateChanged already uses a similar guard.

Re https://github.com/koreader/koreader/pull/8672#discussion_r790126388

NiLuJe/koreader,Frenzie/koreader,koreader/koreader,poire-z/koreader,koreader/koreader,NiLuJe/koreader,poire-z/koreader,Frenzie/koreader