fix sigint handling for viewer sample
fix sigint handling for viewer sample

awslabs/amazon-kinesis-video-streams-webrtc-sdk-c,awslabs/amazon-kinesis-video-streams-webrtc-sdk-c,awslabs/amazon-kinesis-video-streams-webrtc-sdk-c,awslabs/amazon-kinesis-video-streams-webrtc-sdk-c