Fix getCurrentScreenMode() when no window has been created yet

nel/src/3d/driver/opengl/driver_opengl_window.cpp

@@ -2485,13 +2485,19 @@ bool CDriverGL::getCurrentScreenMode(GfxMode &mode)
 	Window child;
 
 	// get window position so we can compare monitors (or mouse position if window not visible yet) 
+	bool useMouseForPosition = true;
+	if (_win != EmptyWindow)
+	{
 		XWindowAttributes xwa;
 		XGetWindowAttributes(_dpy, _win, &xwa);
 		if (xwa.map_state != IsUnmapped)
 		{
 			XTranslateCoordinates(_dpy, _win, xwa.root, xwa.x, xwa.y, &x, &y, &child);
+			useMouseForPosition = false;
 		}
-	else
+	}
+
+	if (useMouseForPosition)
 	{
 		sint rx, ry, wx, wy;
 		uint mask;