[gnome-boxes] libvirt-broker: avoid empty returns in non-void methods

[Felipe Borges <felipeborges src gnome org>]

commit a405a0f8610c4843cbdc07d59c6071870b7cb223
Author: Ernestas Kulik <ernestask gnome org>
Date:   Sat Jan 27 15:53:40 2018 +0200

    libvirt-broker: avoid empty returns in non-void methods
    
    In the spirit of https://bugzilla.gnome.org/show_bug.cgi?id=792942,
    Clang turned these into hard errors.

 src/libvirt-broker.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/libvirt-broker.vala b/src/libvirt-broker.vala
index 831dcde5..2ea89cd8 100644
--- a/src/libvirt-broker.vala
+++ b/src/libvirt-broker.vala
@@ -20,13 +20,13 @@ private LibvirtBroker () {
     }
 
     public GVir.Connection get_connection (string name) {
-        return_if_fail (broker != null);
+        return_val_if_fail (broker != null, null);
         return broker.connections.get (name);
     }
 
     public async LibvirtMachine add_domain (CollectionSource source, GVir.Connection connection, GVir.Domain 
domain)
                                             throws GLib.Error {
-        return_if_fail (broker != null);
+        return_val_if_fail (broker != null, null);
 
         if (pending_domains.find (domain) != null) {
             // Already being added asychronously