Fix incorrect assertion on number of array dimensions.

This has been wrong ever since the support for multi-dimensional
arrays as PL/python function arguments and return values was
introduced in commit 94aceed317.

Backpatch-through: 10
Discussion: https://www.postgresql.org/message-id/61647b8e-961c-0362-d5d3-c8a18f4a7ec6%40iki.fi

src/pl/plpython/plpy_typeio.c

@@ -679,7 +679,7 @@ PLyList_FromArray(PLyDatumToOb *arg, Datum d)
 	/* Array dimensions and left bounds */
 	ndim = ARR_NDIM(array);
 	dims = ARR_DIMS(array);
-	Assert(ndim < MAXDIM);
+	Assert(ndim <= MAXDIM);
 
 	/*
 	 * We iterate the SQL array in the physical order it's stored in the