Fix crash on startup X server is not available (#895)

include/hyperion/GrabberWrapper.h

@@ -51,6 +51,11 @@ public:
 	///
 	virtual void stop();
 
+	///
+	/// Check if grabber is active
+	///
+	virtual bool isActive() const;
+
 	///
 	/// @brief Get a list of all available V4L devices
 	/// @return List of all available V4L devices on success else empty List
@@ -146,6 +151,12 @@ private slots:
 	/// Will start and stop grabber based on active listeners count
 	void handleSourceRequest(const hyperion::Components& component, const int hyperionInd, const bool listen);
 
+	///
+	/// @brief Update Update capture rate
+	/// @param type   interval between frames in millisecons
+	///
+	void updateTimer(int interval);
+
 protected:
 	QString _grabberName;