It seems that certain encoders (quicksync) do not have proper back-end
support in the windows media foundation libraries for certain CPUs.
Quicksync doesn't appear to support CPUs that are not haswell (4xxx) or
above.  It's really annoying, but there's not much we can do about it
until we implement our own custom quicksync implementation.

This check simply makes it attempt to spawn an encoder to check to see
whether the encoder can actually be created before registering an
encoder.