close IOCB if open failed -- otherwise it is still marked as "in use"

You never cease to learn...

On the Atari, if an "open" call fails, the IOCB is still marked to be in use and needs to be closed in order to release it.
This patch implements this for the "open" calls in the runtime library except for the calls in the TGI drivers. There the return status of "open" currently isn't checked at all, which needs to be addressed in the future.