[newlib-cygwin] Cygwin: symlink_info::check: avoid assertion failure

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=48fbe173f403c853e7f9fef128b0228f472e715d

commit 48fbe173f403c853e7f9fef128b0228f472e715d
Author: Ken Brown <kbrown@cornell.edu>
Date:   Mon Dec 9 07:27:18 2019 -0500

    Cygwin: symlink_info::check: avoid assertion failure
    
    On certain error conditions there is a code snippet that checks
    whether the last component of the path has a trailing dot or space or
    a leading space.  Skip this check if the last component is empty,
    i.e., if the path ends with a backslash.  This avoids an assertion
    failure if the trailing backslash is the only backslash in the path,
    as is the case for a DOS drive 'X:\'.
    
    Addresses: https://cygwin.com/ml/cygwin/2019-12/msg00016.html

Diff:
---
 winsup/cygwin/path.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index f610035..b5efd61 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -2895,7 +2895,8 @@ restart:
 	     slow down normal operation.  This extra check only kicks in if
 	     we encountered a STATUS_OBJECT_NAME_NOT_FOUND *and* we didn't
 	     already attach a suffix. */
-	  if (!restarted && !*ext_here && !(mount_flags & MOUNT_DOS))
+	  if (!restarted && !*ext_here && ext_here[-1] != '\\'
+	      && !(mount_flags & MOUNT_DOS))
 	    {
 	      /* Check for trailing dot or space or leading space in
 		 last component. */