BUG/MEDIUM: config: immediately abort if peers section has no name

BUG/MEDIUM: config: immediately abort if peers section has no name

Cyril Bonté reported that despite commit 0dbbf317 which attempted
to fix the crash when a peers section has no name, we still get a
segfault after the error message when parsing the peers. The reason
is that the returned error code is ERR_FATAL and not ERR_ABORT, so
the parsing continues while the section was not initialized.

This is 1.5-specific, no backport is needed.