searchidx: release lock again during v1 batch callback

searchidx: release lock again during v1 batch callback

Relaxing this lock during a v1 --reindex is important to keep
messages showing up in -watch process in a timely manner.
Looks like I deleted an extra line when doing the following
for v2:

	s/xdb->commit_transaction/self->commit_txn_lazy/

Fixes: 35ff6bb106909b1c ("replace Xapian skeleton with SQLite overview DB")