If EOF is reached, recover_remaining_wals() closes recovery->cursor.
The next time it is called, it looks up the next xlog to scan with
vclockset_match(), but the latter will return vclock of the last
scanned xlog unless a new xlog has appeared since the last call.
As a result, the last xlog is scanned three times during recovery:
by recover_follow_local(), hot_standby_f(), and recovery_finalize().
To fix that, let's make recover_remaining_wals() start recovery from
recovery->vclock if it reached EOF while reading the last xlog.

Closes #2768