[newlib-cygwin] Cygwin: pty: Add missing pinfo check in transfer_input().

[Takashi Yano <tyan0@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=2ee8de782b809c83c4261cc6e7e17bdaf31cff96

commit 2ee8de782b809c83c4261cc6e7e17bdaf31cff96
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Mon Aug 14 19:48:12 2023 +0900

    Cygwin: pty: Add missing pinfo check in transfer_input().
    
    The commit 10d083c745dd has a bug that lacks a check for pinfo pointer
    value for master_pid. This causes segmentation fault if the process
    whose pid is master_pid no longer exists. This patch fixes the issue.
    
    Fixes: 10d083c745dd ("Cygwin: pty: Inherit typeahead data between two input pipes.")
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/fhandler/pty.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc
index db3b77ecf..607333f52 100644
--- a/winsup/cygwin/fhandler/pty.cc
+++ b/winsup/cygwin/fhandler/pty.cc
@@ -3835,7 +3835,9 @@ fhandler_pty_slave::transfer_input (tty::xfer_dir dir, HANDLE from, tty *ttyp,
     to = ttyp->to_slave ();
 
   pinfo p (ttyp->master_pid);
-  HANDLE pty_owner = OpenProcess (PROCESS_DUP_HANDLE, FALSE, p->dwProcessId);
+  HANDLE pty_owner = NULL;
+  if (p)
+    pty_owner = OpenProcess (PROCESS_DUP_HANDLE, FALSE, p->dwProcessId);
   if (pty_owner)
     {
       DuplicateHandle (pty_owner, to, GetCurrentProcess (), &to,