Offer switch to designer only if it is available.

db_qbe.php

@@ -176,6 +176,7 @@ function showColumnSelectCell($columns, $column_number, $selected = '')
     if (! empty($tab['fragment'])) {
         $tab['link'] .= $tab['fragment'];
     }
+    if (isset($tab_designer['link'])) {
 ?>
 <div id="visual_builder_anchor" class="notice hide">
 	<span id="footnote_1">
@@ -186,6 +187,9 @@ function showColumnSelectCell($columns, $column_number, $selected = '')
             value="<?php echo __('visual builder'); ?>" onmouseout="this.style.color='#00F'"/></span>
 	</form>
 </div>
+<?php
+    }
+?>
 <form action="db_qbe.php" method="post">
 <fieldset>
 <table class="data" style="width: 100%;">