Kibana version: master

Describe the bug: If fields with different types are selected (used as columns) and the field filter is used, the icons turn into the unknown type icon if they don't match the filter

Steps to reproduce:

1. Go to Discover
2. Add a number and a string field
3. Filter field list by string
4. Number field is shown with question mark icon

Expected behavior:
Selected fields should keep their icons

Screenshots (if relevant):
(see b and c fields)