Display error if there is no search query

[xmedr]

Overview

This requires input in the search field on asset creation/edit by displaying an error message if the user hasn't entered a query.

Closes #250

Notes

A require attribute unfortunately didn't work on the select or the search input element. So instead, I went the route of having that little if statement

Testing Instructions

• Navigate to a project's phase and click Edit Assets at the bottom
• Click the search button without entering a search term
  • Confirm that the search does not run and an error message is displayed
• Click the search button after entering a search term
  • Confirm that the search still works as normal