fix(lib): include headers from OC\Template\Template as well in produced HTML

Otherwise we only take those added through deprecated method C_Util::addHeader, not those of
OC\Template\Template::addHeader, which does nothing

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/private/Template/Template.php

@@ -122,7 +122,7 @@ class Template extends Base implements ITemplate {
 
 			// Add custom headers
 			$headers = '';
-			foreach (\OC_Util::$headers as $header) {
+			foreach (array_merge(\OC_Util::$headers, $this->headers) as $header) {
 				$headers .= '<' . Util::sanitizeHTML($header['tag']);
 				if (strcasecmp($header['tag'], 'script') === 0 && in_array('src', array_map('strtolower', array_keys($header['attributes'])))) {
 					$headers .= ' defer';