iOS: fix crash in auto correction when using unknown font family

If QFont reports a family name that cannot be used to instanciate
a UIFont, we end up trying to insert a nil object to an
NSDictionary. This will raise an exception.

This patch will check that we have a valid UIFont before using it.

Task-number: QTBUG-38018
Change-Id: Id8a2e4afea8c915ff43a7e4680304ba19328f9c2
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
WinRT: Don't use the native thread handle for waiting

There is no guarantee that the handle from std::thread will be valid
when a wait is made. Instead, simply use an elapsed timer and check
if the thread is finished. This prevents an exception from being thrown
when a bad handle is encountered.

Task-number: QTBUG-31397
Change-Id: Ie2a7e6cbfbb27bf1baff779322670d85e92e10dd
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>