Add availabe button check to webengine app

Author: renonick87

examples/webengine/hello-sdl/index.html

@@ -171,6 +171,10 @@
                     };
 
                     if (!this._isButtonSubscriptionRequested && isRpcAllowed(SDL.rpc.enums.FunctionID.SubscribeButton)) {
+                        const availableButtons = this._sdlManager.getRegisterAppInterfaceResponse().getButtonCapabilities().map(function (capability) {
+                            return capability.getNameParam();
+                        });
+
                         // add button listeners
                         const screenManager = this._sdlManager.getScreenManager();
                         const ButtonName = SDL.rpc.enums.ButtonName;
@@ -180,10 +184,14 @@
                                     ButtonName.TUNEUP, ButtonName.TUNEDOWN];
 
                         for (const buttonName of buttonNames) {
-                            await screenManager.addButtonListener(buttonName, this._onButtonListener.bind(this))
-                                .catch((reason) => {
-                                    this._logRegularMessage(`Unable to subscribe to button: ${reason}`);
+                            if (availableButtons.indexOf(buttonName) > 0) {
+                                console.log('Subscribing to', buttonName);
+                                await screenManager.addButtonListener(buttonName, this._onButtonListener.bind(this)).catch(function (err) {
+                                    console.error(err);
                                 });
+                            } else {
+                                console.log('No capability found for button', buttonName);
+                            }
                         }
 
                         this._isButtonSubscriptionRequested = true;