fix(callback): multi-return values for callback method

Resolves #136

imports/callback/client.lua

@@ -50,7 +50,9 @@ local function triggerServerCallback(_, event, delay, cb, ...)
 			return promise:resolve(response and { msgpack.unpack(response) } or {})
 		end
 
-		return cb and cb(response and msgpack.unpack(response))
+        if cb and response then
+            cb(msgpack.unpack(response))
+        end
 	end
 
 	if promise then