trigger NODATA error for invalid InRelease files

trigger NODATA error for invalid InRelease files

With the selfgrown splitting we got the problem of not recovering
from networks which just reply with invalid data like those sending
us login pages to authenticate with the network (e.g. hotels) back.

The good thing about the InRelease file is that we know that it must
be clearsigned (a Release file might or might not have a detached sig)
so if we get a file but are unable to split it something is seriously
wrong, so there is not much point in trying further.

The Acquire system already looks out for a NODATA error from gpgv,
so this adds a new error message sent to the acquire system in case
the splitting we do now ourselves failed including this magic word.

Closes: #712486