crash on invalid or not givin dumppath solved.

ChangeLog

@@ -1,4 +1,5 @@
 2022-11-29:
+- Crash on invalid dumpfile solved.
 - closing and reopening of windows is working now.
 - RGB16 debayer mode simple/bilinear can now be choosen in the settings menu
 

videodev-dumpfile.cc

@@ -82,7 +82,11 @@ int VideoDev_Dumpfile::GetDeviceList(std::list<std::string> *list) {
  * prepare the buffer, InitMMAP and read all controls
  */
 int VideoDev_Dumpfile::Open() {
+	if (config.readdumppath == NULL) return VDEV_STATUS_ERROR;
+
 	std::string fname = config.readdumppath;
+
+
 	fname = fname + "/" + conf_device;
 
 	uint32_t inbuf[3];