Discovered in the QA of T329493.

In T329493#9863795, @dom_walden wrote:

I found a few issues which I don't think are urgent:

• The block form appears when there are no results, so no one to select to block.

Using Special:Log as an example (where the button to suppress log entries is not displayed if the list is empty), we should probably not display the form. Furthermore, if the results are empty the form will open links to Special:InvestigateBlock with no pre-filled targets and so is not providing anything over loading the special page normally.