Fix off-by-one error in cursor hiding/showing function

Incorrect API use according to msdn.

Source: http://msdn.microsoft.com/en-us/library/windows/desktop/ms648396%28v=vs.85%29.aspx
"cursor is displayed only if the display count is greater than or equal to 0"
Merge pull request #1038 from stenyak/fix-cursor-show-bug

Fix off-by-one error in cursor hiding/showing function