[R2.20 Build 64] contrail-vrouter-agent crash while doing router-gateway-clear

Exception causes agent to core.

Steps to recreate:
     1. neutron router-create lr1
     2. neutron router-interface-add lr1 <subnet>
     3. neutron router-gateway-set lr1 public
     4. neutron router-gateway-clear lr1;

Easy way to recreate: to run set and clear in loop.
while true; do neutron router-gateway-set lr1 public; sleep 1; neutron router-gateway-clear lr1; done

Ran vrouter in gdb to catch the exception:
(gdb) catch throw
(gdb) bt
#0 0x00007ffff5e5a910 in __cxa_throw () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1 0x00007ffff5e07987 in std::__throw_out_of_range(char const*) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#2 0x000000000098e1bf in _M_range_check (__n=0, this=<optimized out>) at /usr/include/c++/4.6/bits/stl_vector.h:719
#3 at (this=<optimized out>, __n=<optimized out>) at /usr/include/c++/4.6/bits/stl_vector.h:755
#4 FindAndSetInterfaces (graph=<optimized out>, vm_node=<optimized out>, properties=0x7ffff50b8ba0, svc_instance=<optimized out>) at controller/src/vnsw/agent/oper/service_instance.cc:231
#5 0x000000000098e40c in ServiceInstance::CalculateProperties (this=0x7fffec1c8100, graph=0x7fffe8002930, properties=0x7ffff50b8ba0) at controller/src/vnsw/agent/oper/service_instance.cc:644
#6 0x000000000099146d in CalculateProperties (properties=0x7ffff50b8ba0, graph=0x7fffe8002930, this=0x7fffec1c8100) at controller/src/vnsw/agent/oper/service_instance.cc:633
#7 ServiceInstanceTable::ChangeEventHandler (this=0x7fffe801a6b0, entry=<optimized out>) at controller/src/vnsw/agent/oper/service_instance.cc:766
#8 0x000000000090f0eb in operator() (a0=<optimized out>, this=0x7fffe801abc8) at build/include/boost/function/function_template.hpp:763
#9 IFMapDependencyManager::ProcessChangeList (this=0x7fffe8002a50) at controller/src/vnsw/agent/oper/ifmap_dependency_manager.cc:195
#10 0x000000000101b6ab in operator() (this=<optimized out>) at build/include/boost/function/function_template.hpp:763
#11 TaskTrigger::WorkerTask::Run (this=<optimized out>) at controller/src/base/task_trigger.cc:19
#12 0x0000000001013d45 in TaskImpl::execute (this=0x7ffff0061ac0) at controller/src/base/task.cc:238
#13 0x00007ffff60c3e52 in ?? () from /usr/lib/libtbb.so.2
#14 0x00007ffff60bfc2d in ?? () from /usr/lib/libtbb.so.2
#15 0x00007ffff60bf0db in ?? () from /usr/lib/libtbb.so.2
#16 0x00007ffff60bcc1f in ?? () from /usr/lib/libtbb.so.2
#17 0x00007ffff60bce59 in ?? () from /usr/lib/libtbb.so.2
#18 0x00007ffff62dae9a in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#19 0x00007ffff55c838d in clone () from /lib/x86_64-linux-gnu/libc.so.6
#20 0x0000000000000000 in ?? ()