ReaderToc: Unbreak ToC depth detection (#7569)
ReaderToc: Unbreak ToC depth detection (#7569)

No need to reinvent the wheel.

Fix #7568, regression since #7553
koreader/koreader,NiLuJe/koreader,Frenzie/koreader,NiLuJe/koreader,koreader/koreader,poire-z/koreader,poire-z/koreader,Frenzie/koreader,mwoz123/koreader