Themes: improve search by trimming search string.

Fix an issue where searching installed themes for an empty string resulted in matching all themes.

Props afercia, desrosj, hesyifei, evalarumbe.
Fixes #39041.


git-svn-id: https://develop.svn.wordpress.org/trunk@45557 602fd350-edb4-49c9-b593-d223f7449a82

src/js/_enqueues/wp/theme.js

@@ -180,6 +180,9 @@ themes.Collection = Backbone.Collection.extend({
 		// Start with a full collection
 		this.reset( themes.data.themes, { silent: true } );
 
+		// Trim the term
+		term = term.trim();
+
 		// Escape the term string for RegExp meta characters
 		term = term.replace( /[-\/\\^$*+?.()|[\]{}]/g, '\\$&' );