Only show 'Preview' on the custom header screen if there is something…

… to show.

props nickmomrik.
fixes #14531.

Built from https://develop.svn.wordpress.org/trunk@25135


git-svn-id: http://core.svn.wordpress.org/trunk@25115 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/custom-header.php

@@ -464,6 +464,7 @@ function step_1() {
 <table class="form-table">
 <tbody>
 
+<?php if ( get_custom_header() || display_header_text() ) : ?>
 <tr valign="top">
 <th scope="row"><?php _e( 'Preview' ); ?></th>
 <td>
@@ -490,6 +491,8 @@ function step_1() {
 	<?php } ?>
 </td>
 </tr>
+<?php endif; ?>
+
 <?php if ( current_theme_supports( 'custom-header', 'uploads' ) ) : ?>
 <tr valign="top">
 <th scope="row"><?php _e( 'Select Image' ); ?></th>