handle invalid_actor in sync send + anon_send_exit
handle invalid_actor in sync send + anon_send_exit

this patch checks in anon_send_exit for invalid_actor and
turns it into a NOP if needed, sync_send throws
std::invalid_argument to have at least a defined behavior

tbenthompson/actor-framework,cmaughan/actor-framework,szdavid92/actor-framework,PlexChat/actor-framework,1blankz7/actor-framework,rvlm/actor-framework,DavadDi/actor-framework,szdavid92/actor-framework,rvlm/actor-framework,rvlm/actor-framework,1blankz7/actor-framework,1blankz7/actor-framework,TanNgocDo/actor-framework,cmaughan/actor-framework,tempbottle/actor-framework,actor-framework/actor-framework,firegurafiku/actor-framework,tbenthompson/actor-framework,cmaughan/actor-framework,nq-ebaratte/actor-framework,TanNgocDo/actor-framework,DavadDi/actor-framework,TanNgocDo/actor-framework,1blankz7/actor-framework,actor-framework/actor-framework,DavadDi/actor-framework,firegurafiku/actor-framework,szdavid92/actor-framework,tempbottle/actor-framework,PlexChat/actor-framework,firegurafiku/actor-framework,PlexChat/actor-framework,tempbottle/actor-framework,DavadDi/actor-framework,nq-ebaratte/actor-framework,actor-framework/actor-framework,actor-framework/actor-framework,tbenthompson/actor-framework,nq-ebaratte/actor-framework,nq-ebaratte/actor-framework