Check for unset variable before comparing with -ge, -lt, etc.
Check for unset variable before comparing with -ge, -lt, etc.

Refs #1622.

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