hw/xwin: Bug fixes for screen sizing when the screen window is on a non-primary monitor

There is a bug that when the -screen option is used to specify a monitor for
the screen window to be located on, but no explicit size is specified
(and the -multiplemonitors option isn't specified), the screen
window size is always constrained to fit the work area of the primary
monitor (rather than the work area of the specified monitor)

This gives incorrect results if you want a screen the same size as your
non-primary monitor (e.g. by using -screen 0 @2) and your non-primary
monitor is larger than your primary monitor.

(This can be worked around by specifying -multiplemonitors and an explicit
screen size the same size as the monitor (e.g. -multiplemonitors -screen 0
1600x1200@2))

Fix to use work area for the monitor specified for the screen, rather than the
primary monitor work area (unless -multiplemonitors is used, in which case we
continue to use the virtual desktop work area instead)

Also fix the adjustment for an autohide taskbar, so that it is only done if the
taskbar is on the same monitor as the screen (or -multiplemonitors is used)

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

hw/xwin/winmonitors.c

@@ -48,6 +48,7 @@ getMonitorInfo(HMONITOR hMonitor, HDC hdc, LPRECT rect, LPARAM _data)
         data->monitorOffsetY = rect->top;
         data->monitorHeight = rect->bottom - rect->top;
         data->monitorWidth = rect->right - rect->left;
+        data->monitorHandle = hMonitor;
         return FALSE;
     }
     return TRUE;