Fixed minor file explorer bug.

[tobyoconnell]

To replicate bug:

1. Open two vim buffers.
2. Type lf or lg
3. Type in a bunch of garbage that will not match any files, such as "sanhunehuanhurruhensuohsh"
4. Press any arrow key (up, left, right, down)
5. Ruby NaN or Divide by Zero error is displayed.

Fix: Now pressing any direction key does nothing in this scenario, but works normally otherwise.

[sjbach]

Merged - thanks!