You should remove this part:
<?php if ( (function_exists('has_post_thumbnail')) && (has_post_thumbnail()) ) { ?>
<div class="widget-img">
<a href="https://wordpress.stackexchange.com/questions/116533/<?php the_permalink(); ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_post_thumbnail('lists'); ?></a>
</div><!--widget-img-->
<?php } ?>
.
Just to explain… This conditional statement askes… if there is a thumbnail run the code in between me and my closing tag…
<?php if ( (function_exists('has_post_thumbnail')) && (has_post_thumbnail()) ) { ?>
<?php } ?>
This part “echoes” the thumbnail container (div) & its href wrapper & the thumbnail itself.
<div class="widget-img">
<a href="https://wordpress.stackexchange.com/questions/116533/<?php the_permalink(); ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_post_thumbnail('lists'); ?></a>
</div><!--widget-img-->