Summary:
In certain situations, like infinitepush, the noderev cache builders would try
to save a node that didn't exist in the repo. This caused an exception. Now we
check each node before we attempt to resolve it to a rev.
Test Plan: Added a test. It failed before, and passes now.
Reviewers: #mercurial, andrasbelo
Reviewed By: andrasbelo
Subscribers: andrasbelo, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D4494848
Signature: t1:4494848:1485964835:986d4fe3e29404cac22e4acf7d88c3715fcb51b9
