Disable database logging by default.

It can be re-enabled using --enable-dblog

Until we actually start using this data somewhere there is not much
point in storing it. Since it's already known that writing to the
database can affect I/O performance, especially where drives are
shared with recordings, this could potentially even cause a positive
feedback loop. The I/O starvation causes the backend to start logging
slow read/write warnings, which in turn increase the writes to the
database exacerbating the problems.

The same problem is also true, to a greater or lesser extent with file
based logging but we actually need the file logs so there isn't much
we can do there.
Prevent logging fault when application is not run from absolute path.
(cherry picked from commit 246114bc09de10b0738ac06b8652dcc17e36cea1)
Fix segfault in DecoderBase::PosMapFromEnc() when calling back() on an empty vector. Fixes #10598