[CMake] CPACK_NSIS_MUI_ICON only used when CPACK_NSIS_MUI_UNIICON also set

[Mike McQuaid]

CPACK_NSIS_MUI_ICON can only used when CPACK_NSIS_MUI_UNIICON also set
as the C++ code seems to require them both to have a value. Surely
this could be an || rather than an && here as there's no reason why
the user should have to set both to have one change?

If this is not intentional, let me know and I'll create a patch.

I also filed a bug about this:
http://public.kitware.com/Bug/view.php?id=11143
-- 
Mike McQuaid
http://mikemcquaid.com