the logconfig is properly dimensioned, and only free the channellist
memory in isc_logconfig_destroy if the channellist_count is > 0.
the first addresses a problem that could occur when a successful
isc_log_create was followed immediately by isc_log_[v]write[1] or
isc_log_destroy (with no intervening isc_log_usechannel or
isc_logconfig_use), and the second addresses a problem that could
occur in cleanup if isc_log_create or isc_logconfig_create failed.
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