Replace empty table header with a table cell.

props afercia.
fixes #33047.

git-svn-id: https://develop.svn.wordpress.org/trunk@33456 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/themes.php

@@ -280,7 +280,7 @@ $can_delete = current_user_can( 'delete_themes' );
 		<th><?php _ex('Name', 'theme name'); ?></th>
 		<th><?php _e('Description'); ?></th>
 		<?php if ( $can_delete ) { ?>
-			<th></th>
+			<td></td>
 		<?php } ?>
 		</tr>
 	</tr>