uihelpers: Don't let empty bridge be the default selection

On rethinking, it seems a bit risky that user could create a bogus bridge
and then have all new guests choose it by default and provide no networking.
Be safe and force the user to opt in.

src/virtManager/uihelpers.py

@@ -166,8 +166,8 @@ def populate_network_list(net_list, conn):
 
         if br.is_shared():
             sensitive = True
-            hasShared = True
             if br.get_bridge():
+                hasShared = True
                 brlabel = "(%s)" % pretty_network_desc(nettype, bridge_name)
             else:
                 bridge_name = name