Only use console window size if ioctl(TIOCGWINSZ) succeeded.

[Lastique]

This avoids potentially using uninitialized data if ioctl fails. Also, zero-initialize the winsize struct to begin with.

[Lastique]

This fixes valgrind errors in histogram_ostream_ascii_test, when the test output is redirected to a file. Full valgrind log is below:

vg.log

[HDembinski]

Thanks for investigating and providing a solution, that's awesome.