[newlib-cygwin] Cygwin: build_env: fix off-by-one bug when re-adding PATH

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=472fbb8b97d35fc636be059bf733d390b0671f4d

commit 472fbb8b97d35fc636be059bf733d390b0671f4d
Author: Michael Haubenwallner <michael.haubenwallner@ssi-schaefer.com>
Date:   Wed Aug 7 10:51:16 2019 +0200

    Cygwin: build_env: fix off-by-one bug when re-adding PATH
    
    Adding default winvar 'PATH=C:\cygwin64\binZ' to an environment that is
    already allocated for 'SYSTEMROOT=ZWINDIR=Z', we need to count that
    trailing (Z)ero as well.  Otherwise we trigger this assertion failure:
    
    $ /bin/env -i SYSTEMROOT= WINDIR= /bin/env
    assertion "(s - envblock) <= tl" failed: file "/home/corinna/src/cygwin/cygwin-3.0.7/cygwin-3.0.7-1.x86_64/src/newlib-cygwin/winsup/cygwin/environ.cc", line 1302, function: char** build_env(const char* const*, WCHAR*&, int&, bool, HANDLE)
    Aborted (core dumped)

Diff:
---
 winsup/cygwin/environ.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/environ.cc b/winsup/cygwin/environ.cc
index 1248427..8fa01b2 100644
--- a/winsup/cygwin/environ.cc
+++ b/winsup/cygwin/environ.cc
@@ -1295,7 +1295,7 @@ build_env (const char * const *envp, PWCHAR &envblock, int &envc,
 	 during execve. */
       if (!saw_PATH)
 	{
-	  new_tl += cygheap->installation_dir.Length / sizeof (WCHAR) + 5;
+	  new_tl += cygheap->installation_dir.Length / sizeof (WCHAR) + 5 + 1;
 	  if (new_tl > tl)
 	    tl = raise_envblock (new_tl, envblock, s);
 	  s = wcpcpy (wcpcpy (s, L"PATH="),