Thread local storage (TLS) index leak on windows

qt_current_thread_data_tls_index is created by qt_create_tls() function.

If qt_create_tls() is called by multiple threads at the same time, qt_current_thread_data_tls_index may be created multiple times, and only the last one is saved, the others are leaked.

The code could be changed as follows.

void qt_create_tls()
{
 if (qt_current_thread_data_tls_index != TLS_OUT_OF_INDEXES)
   return;
 static QBasicMutex mutex;
 QMutexLocker locker(&mutex);
 if (qt_current_thread_data_tls_index != TLS_OUT_OF_INDEXES)
   return;
 qt_current_thread_data_tls_index = TlsAlloc();
}