BUG/MINOR: contrib/spoa-server: Do not free reference to NULL

As per https://docs.python.org/3/c-api/refcounting.html, Py_DECREF
should not be called on NULL objects.

This patch must be backported as far as 2.0.

(cherry picked from commit c7d303a0a8962f955e9dd271ee9775dd8eb88cfe)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit dcda9a0cf1d8c381208c426cbf500c7e5f9a3468)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 9aeae8361831612f4f441e0582eabc66c29d1219)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/contrib/spoa_server/ps_python.c b/contrib/spoa_server/ps_python.c
index a8e751f..dd4e63d 100644
--- a/contrib/spoa_server/ps_python.c
+++ b/contrib/spoa_server/ps_python.c
@@ -449,7 +449,6 @@
 		ent = PyDict_New();
 		if (ent == NULL) {
 			Py_DECREF(kw_args);
-			Py_DECREF(ent);
 			PyErr_Print();
 			return 0;
 		}