Missing space when inserting new filter

Created by: eseliger

• Sourcegraph version: master
• Platform information: sourcegraph.com

Steps to reproduce:

1. Enter some repo filter
2. Press space
3. Type 'l'
4. Choose lang filter from suggestions
5. See it works correctly
6. Remove lang filter again
7. Add space after repo filter
8. Use ctrl + space to get suggestions (I think there is some unnecessary delay here also, but just very minor)
9. Choose lang again

Expected behavior:

The filter is added and works

Actual behavior:

It is added by removing the space, hence it's invalid