Well, we still deactivate it when regex is nil, but the function
should not look at previous value of ledger-occur-mode:
- the interactive function (ledger-occur) already do it, we don't need
to do it there,
- caller that want to deactivate the occur stuff only have to call
ledger-occur with a nil regex
- the old behavior make ledger-reconcile to turn off occur stuff if it
was already turn on, when what we do want is that the occur stuff
change to the new account.
cf6a23b2fe