Fix incorrect switch from ! to not ! which happened in commit 064cdb5e, which dealt with

unbuffered stdout.  After that commit 4ce0be75 was added which appeared to bandaid the
fallout making the only place using the unbuffered option was introduced in the former commit and
only really have unbuffered output on a PTY.  The latter commit would potentially send back
unfinished output without a newline causing jumbled output when expecting buffered output thus
resulting in potentially jumbled/unbuffered output.

I was able to reproduce this regularly with test1.31.

In any case making it so the code is clearer to read is a win.