running usb_cam_node does not give proper feedback when using a video device without proper permissions

[lukas-czy]

Issue Description
When attempting to run the usb_cam_node with a /dev/video device without the necessary permissions, the node fails and crashes. The problem lies in the error handling, as the exception is not adequately handled, resulting in a vague error message.

Current Behavior
The current log output when starting the node without proper permission is as follows:

❯ ros2 run usb_cam usb_cam_node_exe
[INFO] [1698243801.072328729] [usb_cam]: camera_name value: default_cam
[WARN] [1698243801.072534313] [usb_cam]: framerate: 30.000000
[INFO] [1698243801.073781020] [usb_cam]: using default calibration URL
[INFO] [1698243801.073798354] [usb_cam]: camera calibration URL: file:///home/vm/.ros/camera_info/default_cam.yaml
[ERROR] [1698243801.073881770] [camera_calibration_parsers]: Unable to open camera calibration file [/home/vm/.ros/camera_info/default_cam.yaml]
[WARN] [1698243801.073921020] [usb_cam]: Camera calibration file /home/vm/.ros/camera_info/default_cam.yaml not found
[INFO] [1698243801.073936645] [usb_cam]: Starting 'default_cam' (/dev/video0) at 640x480 via mmap (yuyv) at 30 FPS
terminate called after throwing an instance of 'char*'
[ros2run]: Aborted

Proposed Solution
Notice: I am not a skilled c++ Developer, so I might be wrong
It appears that a potential solution could involve modifying the usb_cam_node.cpp file. Specifically, you might consider adding a try-catch block around the code segment between line 148 and 156. This try-catch block should provide a more informative error message for cases where proper permissions are lacking.

[flynneva]

Fixed with #286