Only create OSError subclass when two args are used

Author: slozier

Src/IronPython/Runtime/Exceptions/PythonExceptions.cs

@@ -120,7 +120,7 @@ public override string ToString() {
 
         public partial class _OSError {
             public static new object __new__(PythonType cls, [ParamDictionary] IDictionary<string, object> kwArgs, params object[] args) {
-                if (cls == OSError && args.Length >= 1 && args[0] is int errno) {
+                if (cls == OSError && args.Length >= 2 && args[0] is int errno) {
                     if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows)) {
                         if (args.Length >= 4 && args[3] is int winerror) {
                             errno = WinErrorToErrno(winerror);
@@ -139,8 +139,8 @@ public object filename {
                 set { _filename = value; }
             }
 
-            // TODO: hide property on Unix
             private object _winerror = Undefined;
+            [PythonHidden(PlatformsAttribute.PlatformFamily.Unix)]
             public object winerror {
                 get { return ReferenceEquals(_winerror, Undefined) ? null : _winerror; }
                 set { _winerror = value; }