IMP-1339: Fix crash in rcfile scanner from mem-pool tracking bug.

In the case where the MemPool fails in FindChunk, we were not properly
updating the MemPool's state.

Change-Id: I3ed9bd7ee9505cfaf4c7812304c1da85ae06f72f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2160
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins