Workaround for stalled CDC bulk out endpoint
It seems that some events or interrupts are lost. This is a  workaround and a proper solution is in work. But until now this workaround should keep things moving.
Have the build number and date time shown as comment in the html file.
new api function in usb stack to check number of free bytes in bulk out buffers
new api function to get number of free bytes in the output buffers
copy only the number of bytes that can be written