Cygwin: console: ignore NUL byte on write in xterm emulation mode as well

Cygwin: console: ignore NUL byte on write in xterm emulation mode as well

A NUL byte in the output stream got accidentally not handled as IGN char
in xterm console mode.  The internal mbtowc conversion doesn't handle
embedded NUL values gracefully, it always stops converting at NUL bytes.
This broke the output of strings with embedded NUL bytes.

Fix this by always skipping IGN chars in the "normal char output loop"
and make sure not to move the cursor one position to the right, as in
legacy console mode.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>