Fix an error when a set-returning function fails halfway through the execution

If the function using yield to return rows fails halfway, the iterator
stays open and subsequent calls to the function will resume reading
from it.  The fix is to unref the iterator and set it to NULL if there
has been an error.

Jan Urbański

src/pl/plpython/plpython.c

@@ -1164,6 +1164,14 @@ PLy_function_handler(FunctionCallInfo fcinfo, PLyProcedure *proc)
 		Py_XDECREF(plargs);
 		Py_XDECREF(plrv);
 
+		/*
+		 * If there was an error the iterator might have not been exhausted
+		 * yet. Set it to NULL so the next invocation of the function will
+		 * start the iteration again.
+		 */
+		Py_XDECREF(proc->setof);
+		proc->setof = NULL;
+
 		PG_RE_THROW();
 	}
 	PG_END_TRY();