use an if statement to check if the column is blank:
<?php if($row_rsproducts['ProductSizeChart'] != "") { ?>
<div id="gallery1" class="lbGallery1">
<ul>
<li> <a href="../../images/<?php echo $row_rsproducts['ProductSizeChart']; ?>" title="Luckie x Losers">*Size Chart*</a></li>
</ul>
</div>
<?php } ?>