Prevent a crash in QLayout::replaceWidget

Item might be null.

Change-Id: Ia432a35cb1a6bb02ee056ff8ad44a9f35bdbc146
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
NSUrlConnection backend for QNetworkAccessManager

Add support for QNetworkAccessManager https REST on
iOS, without adding a dependency on OpenSSL.

The current limitations are:
- Overriding server certificate trust issues (for
  example expired certificates) is not supported.
- Usage on non-gui threads is not supported.
  NSurlConnection needs a CoreFoundation-based event
  loop, which Qt currently only provides when using
  QGuiApplication on the main thread.

Change-Id: Ic6f74591d40c3b2248ab81db12647e432377cd4f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>