[winswitch] Xpra niggle

[Anthony Stone]

The latest version of xpra behaves much better on startup and closedown
-- thanks for fixing this. There is still a minor peculiarity: on
startup I get the following (Ubuntu 16.04):

...
2018-09-26 10:10:42,832  desktop size is 1920x1080 with 1 screen:
2018-09-26 10:10:42,832   :0.0 (508x285 mm - DPI: 96x96) workarea:
1867x1056 at 53x24
2018-09-26 10:10:42,832     monitor 1 (521x293 mm - DPI: 93x93)
2018-09-26 10:10:42,833  keyboard settings: rules=evdev, model=hpi6,
layout=gb,us
2018-09-26 10:10:42,856 Warning: invalid frame extents value '[0, 0, 28, 0]'
2018-09-26 10:10:42,856  this is probably a bug in 'Compiz'
2018-09-26 10:10:42,856  using '[0, 0, 28, 0]' instead
...

Is the frame extents value '[0, 0, 28, 0]' really invalid? Is this a bug
in Compiz or in xpra?

Anthony