Bail early if we don't have a valid lockfile path

Bail early if we don't have a valid lockfile path

This addresses FS#24292. If one does the bad thing of not checking
pm_errno after calling set_dbpath(), you may not realize the
initialization process went wrong and calling trans_init() resulted in a
segfault. If we don't have a lockfile path, bail out and have
trans_init() fail.

Also remove a ALPM_LOG_FUNC call that was causing pm_errno to return "no
handle"; this was due to a log call in the handle setup (whereby the log
attempts to use a callback attached to the handle).

Signed-off-by: Dan McGee <dan@archlinux.org>