Fix XSS in adm_config_report.php

Yelin and Zhangdongsheng from VenusTech http://www.venustech.com.cn/
reported a vulnerability in the Configuration Report page, allowing an
attacker to inject arbitrary code through a crafted 'config_option'
parameter.

Sanitize the parameter prior to output, to ensure HTML special
characters are properly escaped.

Fixes #22579

adm_config_report.php

@@ -525,7 +525,7 @@ function check_config_value( $p_config ) {
 					<input type="text" name="config_option"
 						value="<?php echo string_attribute( $t_edit_option ); ?>"
 						size="64" maxlength="64" />
-					<input type="hidden" name="original_config_option" value="<?php echo $t_edit_option; ?>" />
+					<input type="hidden" name="original_config_option" value="<?php echo string_attribute( $t_edit_option ); ?>" />
 				</span>
 				<span class="label-style"></span>
 			</div>