searchbar: Make sure we clear highlighting when the last character is removed

We need to call do_find() even if we just backspaced the last character out of
the search entry. This ensures all highlighting gets removed from the document.

xed/xed-searchbar.c

@@ -434,6 +434,7 @@ search_text_entry_changed (GtkEditable *editable,
     else
     {
         search_buttons_set_sensitive (searchbar, FALSE);
+        do_find (searchbar, FALSE);
     }
 }