Fix: illegal memory access in send_viewer_streams

Found by Coverity:

CID 1243037 (#1 of 2): Buffer not null terminated
(BUFFER_SIZE_WARNING)18. buffer_size_warning: Calling strncpy with a
maximum size argument of 4096 bytes on destination array
send_stream.path_name of size 4096 bytes might leave the destination
string unterminated.

CID 1243037 (#2 of 2): Buffer not null terminated
(BUFFER_SIZE_WARNING)18. buffer_size_warning: Calling strncpy with a
maximum size argument of 255 bytes on destination array
send_stream.channel_name of size 255 bytes might leave the destination
string unterminated.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>