bpo-30601: Fix a refleak in WindowsConsoleIO (#2003)

Fix a reference leak in _io._WindowsConsoleIO: PyUnicode_FSDecoder()
always initialize decodedname when it succeed and it doesn't clear
input decodedname object.

Modules/_io/winconsoleio.c

@@ -298,8 +298,7 @@ _io__WindowsConsoleIO___init___impl(winconsoleio *self, PyObject *nameobj,
     self->fd = fd;
 
     if (fd < 0) {
-        PyObject *decodedname = Py_None;
-        Py_INCREF(decodedname);
+        PyObject *decodedname;
 
         int d = PyUnicode_FSDecoder(nameobj, (void*)&decodedname);
         if (!d)