peco/peco — pull request #189 by syohex (2014-09-05 02:28:21+00:00)
Title: Improve verification for custom matcher

This change also avoids run time error(index out of range).

Users may write following configuration by mistake.
Then run time error is not preferable for them.
```json
{
"CustomMatcher": {
"SomeCustomMatcher": [
]
}
}
```