Deleting custom filter manually displays empty chips

## Expected Behavior
Removing the filter from the filter dialog should not display any chips

## Current Behavior
Removing the filter from the filter dialog shows empty chips

## Steps to Reproduce (for bugs)
https://codesandbox.io/s/muidatatables-custom-toolbar-jk556

1. Opening filter dialog (top right)
2. Deleting the age filters by using Backspace key

## Possible workaround
If I return an empty array within the render function of customFilterListOptions as the fallback, it works as expected.
Don't know if this was intended or not.

| Tech | Version |
|--------------|---------|
| Material-UI | 3.2.2 |
| MUI-datatables | 2.14.0 |
| React | 16.4.0 |

Reproduce the empty-chip behavior in the linked CodeSandbox, then trace the customFilterListOptions entry point used by the custom toolbar. Done when deleting the age filters no longer renders empty chips, matching the stated expected behavior and workaround.

Written by the indexing model from the issue text.