Make second arg optional for sdl manager rpc methods

Author: crokita

examples/js/hello-sdl/SDL.min.js

@@ -438,7 +438,9 @@ class SdlManager extends _SdlManagerBase {
             return this.sendRpcResolve(message)
                 .then(result => {
                     messagesRemaining--;
-                    onUpdate(result, messagesRemaining);
+                    if (typeof onUpdate === 'function') {
+                        onUpdate(result, messagesRemaining);
+                    }
                     return result;
                 });
         });
@@ -474,7 +476,9 @@ class SdlManager extends _SdlManagerBase {
             const result = await this.sendRpcResolve(message)
                 .then(result => {
                     messagesRemaining--;
-                    onUpdate(result, messagesRemaining);
+                    if (typeof onUpdate === 'function') {
+                        onUpdate(result, messagesRemaining);
+                    }
                     return result;
                 });
             resolvedRpcs.push(result);