Get screen dimensions directly from screen driver - without use of
a channel!

        SCRXY sizex%, sizey%

Where sizex%/sizey% are return parameters only

Only parameter errors returned.

Note: This has only been tested on SMSQ/E. I dont know if it is valid for

Software status:

V0.01, pjw, 26 Oct 2018
V0.02, pjw, June 5th 2019, check parameters, now Qdos+PI compatible?

Conditions and disclaimer as per