Request Device and Key, when OMEMO is in use

Profanity requests the device list and keys for contacts, also when the user
hasn't generated the OMEMO key. If the user has no OMEMO key, there is no need
to request OMEMO information.

Issue: #1332

src/omemo/omemo.c

@@ -403,6 +403,7 @@ omemo_start_sessions(void)
 void
 omemo_start_session(const char *const barejid)
 {
+    if( omemo_loaded() ) {
         log_info("OMEMO: start session with %s", barejid);
         GList *device_list = g_hash_table_lookup(omemo_ctx.device_list, barejid);
         if (!device_list) {
@@ -416,6 +417,7 @@ omemo_start_session(const char *const barejid)
         for (device_id = device_list; device_id != NULL; device_id = device_id->next) {
             omemo_bundle_request(barejid, GPOINTER_TO_INT(device_id->data), omemo_start_device_session_handle_bundle, free, strdup(barejid));
         }
+    }
 }
 
 void