VCL: Fix for vppcom_session_listen() q_len <= 0 crash
VCL: Fix for vppcom_session_listen() q_len <= 0 crash

Change-Id: I089dd3855fc21b26a125ee392c7548d44b5732b8
Signed-off-by: Keith Burns (alagalah) <469d26a9115c63bc10d4323e29088530ee1e798d@gmail.com>

vpp-dev/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp