use an if statement around each link, for example:
<?php if($row_WADAproduct['ProductZoom'] == "") { ?>
<a href="<?php echo $row_WADAproduct['ProductZoom']; ?>" class="MagicZoomPlus" id="Zoomer" title="<?php echo $row_WADAproduct['ProductName']; ?> Rug"><img src="<?php echo $row_WADAproduct['ProductImage']; ?>"/></a>
<?php } ?>