QNetworkAccessManager - ensure abort reaches QFtp

Previously, we just disconnected signals from QFtp and allowed it
to continue downloading in the background.

Task-number: QTBUG-25494
Change-Id: I891c2fff88ef1ee554d1ccf821a3f7998eeb8406
Reviewed-by: Martin Petersson <Martin.Petersson@nokia.com>

src/network/access/qnetworkaccessftpbackend.cpp

@@ -107,6 +107,9 @@ QNetworkAccessFtpBackend::QNetworkAccessFtpBackend()
 
 QNetworkAccessFtpBackend::~QNetworkAccessFtpBackend()
 {
+    //if backend destroyed while in use, then abort (this is the code path from QNetworkReply::abort)
+    if (ftp && state != Disconnecting)
+        ftp->abort();
     disconnectFromFtp();
 }