no Searchbar placeholder text shown for locked/hidden Tokens

When the Filtered Search bar is empty, but contains only locked tokens, the x is visible and the placeholder text is hidden.

Since making the tokens hidden in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2912 the effect of this is more pronounced

Filtered search manager checks for getSearchQuery. This should be changed to only check for search text or visible tokens