The goal of webcam updater class is to update image in parallel, so all calls
to fetch image invoked on webcam instance will be non-blocking (will return
immediately).
Return currently available image. This method will return immediately
while it was been called after camera has been open. In case when there
are parallel threads running and there is a possibility to call this
method in the opening time, or before camera has been open at all, this
method will block until webcam return first image. Maximum blocking time
will be 10 seconds, after this time method will return null.