Restore rs2html() $htmlspecialchars param behavior

Regression introduced by bda6e1e.

Fixes #968, PR #969

Signed-off-by: Damien Regad <dregad@mantisbt.org>

Changes from original contribution:
- extract trim() call from if statement
- revised commit message
- backport to hotfix/5.22 branch

tohtml.inc.php

@@ -141,7 +141,10 @@ function mime_content_type ($file) {
 
 			default:
 				if ($v) {
-					$v = htmlspecialchars(stripslashes(trim($v)));
+					$v = trim($v);
+					if ($htmlspecialchars) {
+						$v = htmlspecialchars($v);
+					}
 				} elseif ($v === null) {
 					$v = '(NULL)';
 				} else {