Cygwin: pty: Fix failure to clear switch_to_nat_pipe flag.

Cygwin: pty: Fix failure to clear switch_to_nat_pipe flag.

After the commit fbfea31dd9b9, switch_to_nat_pipe is not cleared
properly when non-cygwin app is terminated in the case where the
pseudo console is disabled. This is because get_winpid_to_hand_over()
sometimes returns PID of cygwin process even though it should return
only PID of non-cygwin process. This patch fixes the issue by adding
a new argument which requests only PID of non-cygwin process to
get_console_process_id().

Fixes: fbfea31dd9b9 ("Cygwin: pty: Avoid cutting the branch the pty master is sitting on.")
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>