Names with spaces break issue filter bar.

In 9.3 RC4, after selecting author:@mikegreiling in the filter bar, it automatically gets translated into "Mike Greiling" complete with avatar, but then after submission this ends up being treated as two separate words:

before submit:

Screen_Shot_2017-06-20_at_3.54.52_PM

after submit:

Screen_Shot_2017-06-20_at_3.55.00_PM

the request url contains the following query string:

&state=opened&author_username=Mike&search=Greiling+merge+request

so the error must be when the query string is compiled (as opposed to when the filter bar contents are re-rendered on the resulting page)

/cc @ClemMakesApps (since I know you work on the filter bar quite a bit... not sure if these changes were yours 😄)