wxGUI/nviz: add missing sys module (merge from devbr6, https://trac.osgeo.org/grass/changeset/32868)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@32869 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/nviz.py

@@ -19,6 +19,8 @@ for details.
 
 errorMsg = ''
 
+import sys
+
 import wx
 try:
     from wx import glcanvas