Merge pull request facebookarchive#626 from lutskanu/master

Fixed issue when Notice "Undefined variable: header" occured on PHP 7.0

Author: SammyK

src/Facebook/Url/FacebookUrlDetectionHandler.php

@@ -95,7 +95,8 @@ protected function protocolWithActiveSsl($protocol)
     protected function getHostName()
     {
         // Check for proxy first
-        if ($header = $this->getHeader('X_FORWARDED_HOST') && $this->isValidForwardedHost($header)) {
+        $header = $this->getHeader('X_FORWARDED_HOST');
+        if ($header && $this->isValidForwardedHost($header)) {
             $elements = explode(',', $header);
             $host = $elements[count($elements) - 1];
         } elseif (!$host = $this->getHeader('HOST')) {