Handle sync request where no groups are sent

If a user has no groups, no group sync message is sent. This is a normal
result that should result in a success event rather than a timeout.

// FREEBIE

libtextsecure/sync_request.js

@@ -43,7 +43,11 @@
             }
         },
         onTimeout: function() {
-            this.dispatchEvent(new Event('timeout'));
+            if (this.contactSync || this.groupSync) {
+                this.dispatchEvent(new Event('success'));
+            } else {
+                this.dispatchEvent(new Event('timeout'));
+            }
             this.cleanup();
         },
         cleanup: function() {