Calling nvctrl XNVCTRLIsNvScreen with X display ID used for screen id is
a programmer error. For most common use cases, Gnome on X11 may launch
user sessions on X display ":1" but still uses screen 0. Current code
will always fail to find a correct display in this case, as both
`IsNvScreen(":0", 0)` and `IsNvScreen(":1", 1)` returns false.
Call XDefaultScreen with `struct Display *` to obtain the correct screen
id, then use this id for `IsNvScreen()`.
Tianhao Chai
jackun