Fix a bug where PhabricatorPasteQuery incorrectly rekeys results

Summary: I made changes here recently to improve robustness in the presence of missing files, but accidentally caused the results to re-key. Some callers depend on the mapping, and every other query is consistent about it. Restore the original behavior.

Test Plan: Pnnn works again in remarkup.

Reviewers: dctrwatson, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6134