applier: fix assertion failure after split brain

After receiving async transaction from an old term applier_apply_tx
exits without unlocking the latch. If the same applier tries to
subscribe for replication, it fails with assertion, as the latch is
already locked.

Let's fix the function, which raises error so that it just sets
diag and returns -1.

Closes #10073

NO_DOC=bugfix
NO_CHANGELOG=no crash on release version