[newlib-cygwin] Cygwin: path_conv::eq_worker: add NULL pointer checks

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=22d1ebacfc5a1d3596d5dc25c2464fa51ed58944

commit 22d1ebacfc5a1d3596d5dc25c2464fa51ed58944
Author: Ken Brown <kbrown@cornell.edu>
Date:   Sat Nov 14 09:02:43 2020 -0500

    Cygwin: path_conv::eq_worker: add NULL pointer checks
    
    Don't call cstrdup on NULL pointers.
    
    This fixes a crash that was observed when cloning an fhandler whose
    path_conv member had freed its strings.

Diff:
---
 winsup/cygwin/path.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/path.h b/winsup/cygwin/path.h
index b94f13df8..0b3e72fc1 100644
--- a/winsup/cygwin/path.h
+++ b/winsup/cygwin/path.h
@@ -320,9 +320,11 @@ class path_conv
        contrast to statically allocated strings.  Calling device::dup()
        will duplicate the string if the source was allocated. */
     dev.dup ();
-    path = cstrdup (in_path);
+    if (in_path)
+      path = cstrdup (in_path);
     conv_handle.dup (pc.conv_handle);
-    posix_path = cstrdup(pc.posix_path);
+    if (pc.posix_path)
+      posix_path = cstrdup(pc.posix_path);
     if (pc.wide_path)
       {
 	wide_path = cwcsdup (uni_path.Buffer);