x11/tilda: Fix OOB write in start_default_shell()

The fix was committed to upstream in May 9, but no release was made
for it until now.

https://github.com/lanoxx/tilda/commit/51a980a55ad6d750daa21d43a66d44577dad277b

Update Makefile to make portlint happy

PR: 264270
Reported by: <iron.udjin@gmail.com>
Tested by: <iron.udjin@gmail.com>