Catch storage not available in versions expire command

External storage with session credentials is not accessible without a
user session, hence background jobs and CLI commands can't work with
them. The previously unhandled exception causes logged errors in the
nextcloud log. This patch catches the specific exception and logs it as
warnings. So for a production instance the error won't spam their logs
for this non-recoverable and technically unsolvable error if the minimum
log level is set to the default of 3 (error).

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>