Assert parallel_sync data is non-empty
Assert parallel_sync data is non-empty

We use the data size to determine who we aren't sending to; we can't
distinguish between a non-send and a send-of-nothing.

dschwen/libmesh,jwpeterson/libmesh,hrittich/libmesh,pbauman/libmesh,giorgiobornia/libmesh,roystgnr/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,dschwen/libmesh,roystgnr/libmesh,giorgiobornia/libmesh,pbauman/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,pbauman/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,dschwen/libmesh,pbauman/libmesh,libMesh/libmesh,roystgnr/libmesh,libMesh/libmesh,BalticPinguin/libmesh,libMesh/libmesh,90jrong/libmesh,90jrong/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,giorgiobornia/libmesh,BalticPinguin/libmesh,90jrong/libmesh,libMesh/libmesh,hrittich/libmesh,capitalaslash/libmesh,hrittich/libmesh,pbauman/libmesh,90jrong/libmesh,pbauman/libmesh,dschwen/libmesh,pbauman/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,roystgnr/libmesh,libMesh/libmesh,giorgiobornia/libmesh,pbauman/libmesh,hrittich/libmesh,giorgiobornia/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,giorgiobornia/libmesh,dschwen/libmesh,libMesh/libmesh,jwpeterson/libmesh,roystgnr/libmesh,hrittich/libmesh,90jrong/libmesh,capitalaslash/libmesh,90jrong/libmesh,BalticPinguin/libmesh,hrittich/libmesh,dschwen/libmesh,roystgnr/libmesh,roystgnr/libmesh,hrittich/libmesh,90jrong/libmesh,giorgiobornia/libmesh,90jrong/libmesh,hrittich/libmesh,BalticPinguin/libmesh,90jrong/libmesh,giorgiobornia/libmesh,hrittich/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,BalticPinguin/libmesh,giorgiobornia/libmesh,pbauman/libmesh