R1:5daf08048be0

Fix path autocomplete

Summary: Paths autocompleter sometimes omits `/`.

Test Plan:
# Go to https://secure.phabricator.com/owners/new/.
# Write `/specs/h` to path.
# Delete the second slash resulting in `/specsh`.
# Don't find `/specshistorytest.html` in autocomplete.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2981