[newlib-cygwin] Fixed crash on wine by adding NULL check after memchr

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=4ddf5903fd24feaa6f75ffb12f9cafdd266b386a

commit 4ddf5903fd24feaa6f75ffb12f9cafdd266b386a
Author: Arseniy Lartsev <arseniy@alumni.chalmers.se>
Date:   Tue Jan 7 16:34:39 2020 +0100

    Fixed crash on wine by adding NULL check after memchr
    
    This is not a joke, there are vendors out there who build software for cygwin
    only. Besides, this NULL check is good to have anyway.

Diff:
---
 winsup/cygwin/path.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index b5efd61..c8e73c6 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -4307,6 +4307,8 @@ find_fast_cwd_pointer ()
   const uint8_t *use_cwd = rcall + 5 + offset;
   /* Find first `push %edi' instruction. */
   const uint8_t *pushedi = (const uint8_t *) memchr (use_cwd, 0x57, 32);
+  if (!pushedi)
+    return NULL;
   /* ...which should be followed by `mov crit-sect-addr,%edi' then
      `push %edi', or by just a single `push crit-sect-addr'. */
   const uint8_t *movedi = pushedi + 1;