examples: check value returned by ftell()

Problem detected by the Coverity tool
CID 1042546 (#1 of 1): Argument cannot be negative (NEGATIVE_RETURNS)3.
negative_returns: "initial_pos" is passed to a parameter that cannot be
negative.

fseek(3) can't be called with a negative offset with SEEK_SET
Windows: Add support for VIA VL805 USB 3.0 Host Controllers

* These controllers identify themselves as VUSB3HUB
* Closes #152