winrt: Fix potential crash when reading closed sockets

Using multiple concurrent requests can cause a delay between a socket
closing and getting deleted. At that point the state was closingDown,
but not wasDeleted yet. Especially on slower arm devices, callbacks are
done from another thread causing synchronization issues.

Hence closingDown needs to be synced and handleReadyRead needs to have
more criterias to return early to avoid invalid access crashes.

Easiest to reproduce is heavy scrolling on the mapviewer example when it
downloads a huge amount of tiles and cancels those requests when not in
view anymore.

Change-Id: I442b6243bbefb3af938b6b1b3739a6a85b4887c0
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

0 files changed, 0 insertions, 0 deletions