Coverity analysis defect 24463: Unchecked return value

A new defect has been detected and assigned to greg_10gen in Coverity Connect.
http://coverity.mongodb.com//sourcebrowser.htm?projectId=10001#mergedDefectId=24463
The defect was flagged by checker CHECKED_RETURN in
file /src/mongo/db/geo/r2_region_coverer.cpp
function mongo::R2RegionCoverer::expandChildren(mongo::R2RegionCoverer::Candidate *)
and this ticket was created by milkie