ref count correction for transfer

Crash due to a race condition between this ref correction https://dev.iopsys.eu/voice/asterisk/-/blob/devel/channels/chan_pjsip.c#L2088-2095 and the unref under chan_voicemngr_attended_call_transfer https://dev.iopsys.eu/voice/asterisk-chan-voicemngr/-/blob/devel/src/channels/chan_voicemngr.c?ref_type=heads#L5646-5651 . When the correction happend and finished before the unref during the transfer, which leading the result of ref=1 after the unref, then the crash happened during hangup the channel, add an extra correction for ref<2 could resolve this issue.