Created attachment 4963 
patch to update _NET_DESKTOP_GEOMETRY from monitor/resize events as well

When the screen is resized (i.e. a display is disabled or enabled via xrandr), xfwm4 does not seem to update the _NET_DESKTOP_GEOMETRY hint, which is used by libwnck's pager widget (used by xfce4-panel pager plugin) to figure out how to layout the miniature workspaces

For me this became a problem as I use gdm as DM which always enables both my displays, but after logging into Xfce I have only one enabled. The workspace switcher would then still display very wide miniatures as if both were enabled (presumably because xfwm4 is started before the second display is turned off, so the old value remains in _NET_DESKTOP_GEOMETRY)

I wrote a patch that calls initNetDesktopInfo() (hints.c) from both monitors_changed_cb() and size_changed_cb() (events.c) so that the hint gets updated. I've tested it against xfwm4-4.10.0 and encountered no issues, but it applies cleanly to git master as well. (I wasn't able to compile git master though since I think I need to update some other xfce lib - was getting some missing header errors)

Bug 7511 is related to this and Ashish Myles' comment there is what I based this patch on