Allow empty bridges in interface xml.

src/conf/interface_conf.c

@@ -557,12 +557,13 @@ virInterfaceDefParseBridge(virConnectPtr conn, virInterfaceDefPtr def,
 
     bridge = ctxt->node;
     nbItf = virXPathNodeSet(conn, "./interface", ctxt, &interfaces);
-    if (nbItf <= 0) {
+    if (nbItf < 0) {
         virInterfaceReportError(conn, VIR_ERR_XML_ERROR,
-                                "%s", _("bridge has no interfaces"));
+                                "%s", _("bridge interfaces"));
         ret = -1;
         goto error;
     }
+    if (nbItf > 0) {
         if (VIR_ALLOC_N(def->data.bridge.itf, nbItf) < 0) {
             virReportOOMError(conn);
             ret = -1;
@@ -580,6 +581,7 @@ virInterfaceDefParseBridge(virConnectPtr conn, virInterfaceDefPtr def,
             }
             def->data.bridge.itf[i] = itf;
         }
+    }
 
 error:
     VIR_FREE(interfaces);