Fixing an issue with embedded images

Fixed the issue with html parsing when there was an embedded base64
encoded image in the source - which resulted in regexp errors (too long
regexp).

class.phpmailer.php

@@ -2910,11 +2910,7 @@ public function msgHTML($message, $basedir = '', $advanced = false)
                     }
                     $cid = md5($url) . '@phpmailer.0'; // RFC2392 S 2
                     if ($this->addStringEmbeddedImage($data, $cid, '', 'base64', $match[1])) {
-                        $message = preg_replace(
-                            '/' . $images[1][$imgindex] . '=["\']' . preg_quote($url, '/') . '["\']/Ui',
-                            $images[1][$imgindex] . '="cid:' . $cid . '"',
-                            $message
-                        );
+                    	  $message = str_replace($images[0][$imgindex], $images[1][$imgindex] . '="cid:' . $cid . '"', $message);
                     }
                 } elseif (!preg_match('#^[A-z]+://#', $url)) {
                     // Do not change urls for absolute images (thanks to corvuscorax)