[PocketBook] fix: Crash loading file extensions (#9327)
[PocketBook] fix: Crash loading file extensions (#9327)

In some versions of the /ebrmain/config/extensions.cfg file there is a
comment #ebrcfg. This will not match the regex and crashes koreader as
the table is empty.
Add a check to ensure the table is not empty while reading extensions
from the default file.
Frenzie/koreader,koreader/koreader,NiLuJe/koreader,poire-z/koreader,koreader/koreader,NiLuJe/koreader,poire-z/koreader,Frenzie/koreader