net/cxgbe: fix crash when accessing empty Tx mbuf list
net/cxgbe: fix crash when accessing empty Tx mbuf list

Ensure packets are available before accessing the mbuf list in Tx
burst function. Otherwise, just reclaim completed Tx descriptors and
exit.

Fixes: b1df19e43e1d ("net/cxgbe: fix prefetch for non-coalesced Tx packets")
Cc: stable@dpdk.org

Reported-by: Brian Poole <6701aa5cab8f4633c683a7cc48c7bd998b545f92@gmail.com>
Signed-off-by: Rahul Lakkireddy <3a6b348815dc68871481a310c146a6b821ba8f72@chelsio.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk