Trim search query to prevent searching for empty string

[stephanebisson]

Phabricator Link: https://phabricator.wikimedia.org/T272276

Problem Statement

Searching for empty string returns no results

Solution

Trim the search query and only search if it is not empty

Note

[hueitan]

I think these two scenarios are fine

1. Type , then hit back key, it shows exit confirm dialog, cancel the dialog will remove all
2. Type , then type another digit a, will clear previous

[hueitan]

what about this case

1. Type president obama
2. user want to research for president xxx, then he deletes obama
3. Once the cursor reach o, hit delete will bring the cursor to t, not the empty space there