Issue #9566: Fix a compiler warning on Windows 64-bit in namespace_init()

The result type is int, return -1 to avoid a compiler warning (cast Py_ssize_t
to int).  PyObject_Size() can only fail with -1, and anyway a constructor
should return -1 on error, not an arbitrary negative number.

Objects/namespaceobject.c

@@ -44,7 +44,7 @@ namespace_init(_PyNamespaceObject *ns, PyObject *args, PyObject *kwds)
     if (args != NULL) {
         Py_ssize_t argcount = PyObject_Size(args);
         if (argcount < 0)
-            return argcount;
+            return -1;
         else if (argcount > 0) {
             PyErr_Format(PyExc_TypeError, "no positional arguments expected");
             return -1;