SQUASH/shell.c: @oni-link fix, NULL output
SQUASH/shell.c: reuse klibs kv_roundup32
SQUASH/shell.c: prevent hanging procs witht input

When calling system('cat -', ['some', 'list']), vanilla vim (before a recent
patch that added support for passing lists) and nvim master just pass an
empty file to the process. This is the same as immediately closing the pipe,
which this patch does. If we wouldn't close the pipe, the process will
linger forever (as is the case with `cat -`).
SQUASH/shell.c: remove spurious logs
SQUASH/eval.c: remove spurious logs
SQUASH/eval.c: fix brace
SQUASH/job.c: remove spurious logs and comments