Get rid of double html parsing during render

[MAILPOET-1797]

lib/Util/CSS.php

@@ -35,7 +35,6 @@ class CSS {
   */
   function inlineCSS($url, $contents=null) {
     $html = \pQuery::parseStr($contents);
-
     if (!is_object($html)) {
       return false;
     }
@@ -124,7 +123,7 @@ class CSS {
     }
 
     // Let simple_html_dom give us back our HTML with inline CSS!
-    return (string)$html;
+    return $html;
   }
 
   function parseCSS($text) {