List has duplicates

### Description
While typing in a file path, the list shown has duplicates

### Steps to Reproduce
1. start typing the file path

**Expected behavior:**
Files should only be showed once

**Actual behavior:**
Some files are shown twice(.jpg).

**Reproduces how often:** [What percentage of the time does it reproduce?]
100%

### Versions
Ubuntu 17.04
Atom : 1.21.1
Electron: 1.6.15
Chrome : 56.0.2924.87
Node : 7.4.0
apm 1.18.5
npm 3.10.10
node 6.9.5 x64
python 2.7.13
git 2.11.0

Start by reproducing the duplicate file suggestions while typing a path on the reported Atom setup, then trace the autocomplete-paths code that builds the displayed list. The fix is complete when each matching file, including .jpg files, appears only once and the reproduction no longer occurs.

Written by the indexing model from the issue text.