FIX Add one to current colspan in fixColumns instead of resetting to 2

In the previous situation, the 'No items found' row would be hardcapped at colspan=2. This change ensures that that row always spans all columns in the table

client/src/legacy/GridField.js

@@ -12,6 +12,7 @@ import '../../../thirdparty/jquery-entwine/jquery.entwine.js';
 $.entwine('ss', function($) {
   $('.grid-field').entwine({
     onmatch: function () {
+      // Adds an actions column for the search action if it does not exist already
       if (this.needsColumnFix()) {
         this.fixColumns();
         this.injectSearchButton(false);
@@ -176,7 +177,8 @@ $.entwine('ss', function($) {
       this.find('.sortable-header').append('<th class="main col-Actions" />');
       this.find('tbody tr').each(function () {
         var cell = $(this).find('td:last');
-        cell.attr('colspan', 2);
+        var colspan = cell.attr('colspan') ?? 1;
+        cell.attr('colspan', colspan + 1);
       });
       var $extraCell = $('<th class="extra" />');
       $('.grid-field__filter-header th:last .action').each(function() {