core, plugins: host.getClient now raise an exception instead of returning None when no profile is found, plugins have been adapted consequently and a bit cleaned

src/plugins/plugin_xep_0092.py

@@ -58,8 +58,6 @@ class XEP_0092(object):
                  - os: operating system of the queried entity
         """
         client = self.host.getClient(profile_key)
-        if not client:
-            raise exceptions.ProfileUnknownError
         iq_elt = compat.IQ(client.xmlstream, 'get')
         iq_elt['to'] = jid_.full()
         query_elt = iq_elt.addElement("query", NS_VERSION)