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.
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 25ff247..a294332 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -169,6 +169,7 @@
 static PyObject *
 bytesio_flush(bytesio *self)
 {
+    CHECK_CLOSED(self);
     Py_RETURN_NONE;
 }