Buffer objects would return the read or write buffer for a wrapped object when

the char buffer was requested.  Now it actually returns the char buffer if
available or raises a TypeError if it isn't (as is raised for the other buffer
types if they are not present but requested).

Not a backport candidate since it does change semantics of the buffer object
(although it could be argued this is enough of a bug to bother backporting).

Modules/arraymodule.c

@@ -1787,6 +1787,7 @@ static PyBufferProcs array_as_buffer = {
 	(readbufferproc)array_buffer_getreadbuf,
 	(writebufferproc)array_buffer_getwritebuf,
 	(segcountproc)array_buffer_getsegcount,
+	NULL,
 };
 
 static PyObject *