Filtering commits does not work when using mouse with autocomplete

[pavelevap]

Steps to reproduce:

1. Click into "Search" field on VersionPress admin page, autocomplete popup appears.
2. Select Modifiers - action, then "post/update" (use only mouse).
3. Click "Search" button (or you can use Enter on keyboard).

Commits are not filtered, XHR request: wp-json/versionpress/commits?1557497758499&page=0&query=

When you follow same steps only with keyboard, especially selecting values from autocomplete list (with arrow keys and Enter), everything works well, XHR request: wp-json/versionpress/commits?1557498071657&page=0&query=action%253Apost%252Fupdate%2520

When there are no commits to show, status 500 should appear?