Issue #7865: The close() method of :mod:io objects should not swallow

exceptions raised by the implicit flush().  Also ensure that calling
close() several times is supported.  Patch by Pascal Chambon.

Modules/_io/bytesio.c

@@ -169,6 +169,7 @@ PyDoc_STRVAR(flush_doc,
 static PyObject *
 bytesio_flush(bytesio *self)
 {
+    CHECK_CLOSED(self);
     Py_RETURN_NONE;
 }