Don't SIGINT ourselves on bad daemon data

Summary:
If daemon data is mangled, `bin/phd restart` will SIGINT process `0`, which kills it.

uh oh T.T so sad

Test Plan: Used `bin/phd start` to start daemons; removed PID information from one; saw `bin/phd stop` shut down cleanly and not kill itself.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: mholden, epriestley

Differential Revision: https://secure.phabricator.com/D10308