BUG/MEDIUM: mworker: fix segv in early failure of mworker mode with peers

During an early failure of the mworker mode, the
mworker_cleanlisteners() function is called and tries to cleanup the
peers, however the peers are in a semi-initialized state and will use
NULL pointers.

The fix check the variable before trying to use them.

Bug revealed in issue #1956.

Could be backported as far as 2.0.
1 file changed