windows: always work around EINVAL in case of broken pipe for stdout / stderr
In 29a905fe23ae, I missed the fact that the `winstdout` class works around two unrelated bugs (size limit when writing to consoles and EINVAL in case of broken pipe) and that the latter bug happens even when no console is involved. When writing a test for this, I realized that the same problem applies to stderr, so I applied the workaround for EINVAL to both stdout and stderr. The size limit is worked around in the same case as before (consoles on Windows on Python 2). For that, I changed the `winstdout` class.