Cygwin: pty: Fix handle leak in master process.

If non-cygwin process is started in pty, closing from_master_nat
pipe handle was missing in fhandler_pty_slave::input_transfer().
This occured because the handle was duplicated but not closed.

#198

Fixes: 29431fc ("Cygwin: pty: Inherit typeahead data between two input pipes.")
Reported-by: Hakkin Lain
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/cygwin/fhandler/pty.cc

@@ -4015,6 +4015,7 @@ fhandler_pty_slave::transfer_input (tty::xfer_dir dir, HANDLE from, tty *ttyp,
 	    transfered = true;;
 	}
     }
+  CloseHandle (to);
 
   /* Fix input_available_event which indicates availability in cyg pipe. */
   if (dir == tty::to_nat) /* all data is transfered to nat pipe,