SR-mpls: do not pass empty label stack to fib
SR-mpls: do not pass empty label stack to fib

Change-Id: Ib1601d01a54296e72be3bbfa057fce965549b02b
Signed-off-by: Neale Ranns <b9c0e9ef0223633bc2f318425f615cf5840a0be7@cisco.com>

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