Fix imap_reopen 'mailbox not found' error

When this method was called and tried to reopen the imap connection, an
error was thrown because the second argument must be the complete
mailbox path and not only mailbox name
(http://lu.php.net/manual/fr/function.imap-reopen.php).

src/Fetch/Server.php

@@ -260,7 +260,7 @@ protected function setImapStream()
         {
                 if(isset($this->imapStream))
                 {
-                        if(!imap_reopen($this->imapStream, $this->mailbox, $this->options, 1))
+                        if(!imap_reopen($this->imapStream, $this->getServerString(), $this->options, 1))
                                 throw new \RuntimeException(imap_last_error());
                 }else{
                         $imapStream = imap_open($this->getServerString(), $this->username, $this->password, $this->options, 1);