Cygwin: pty: Revise code waiting for forwarding again.

- After commit 6cc299f0e2, outputs of
  cygwin programs which call both printf() and WriteConsole() are
  frequently distorted. This patch fixes the issue.

winsup/cygwin/tty.cc

@@ -246,6 +246,7 @@ tty::init ()
   term_code_page = 0;
   need_redraw_screen = false;
   fwd_done = NULL;
+  pcon_last_time = 0;
 }
 
 HANDLE