[PATCH] add missing null check in duplicate_buffered_stream()

[Emanuele Torre]

This was causing crashes when non-interactive shells that read stdin,
either source a file that dups stdin, or run an eval command that dups
stdin:

  $ bash <<< 'echo hi 9<&0'
  hi
  $ printf %s\\n 'echo hi 9<&0' > file; bash <<< '. ./file'
  Segmentation fault (core dumped)
  $ bash <<< 'eval "echo hi 9<&0"'
  Segmentation fault (core dumped)
---
 input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/input.c b/input.c
index 6eab9909..8c7756a9 100644
--- a/input.c
+++ b/input.c
@@ -359,7 +359,7 @@ duplicate_buffered_stream (int fd1, int fd2)
       buffers[fd2]->b_flag |= B_WASBASHINPUT;
     }
 
-  if (fd_is_bash_input (fd1) || (buffers[fd1] && (buffers[fd1]->b_flag & 
B_SHAREDBUF)))
+  if (buffers[fd2] && fd_is_bash_input (fd1) || (buffers[fd1] && 
(buffers[fd1]->b_flag & B_SHAREDBUF)))
     buffers[fd2]->b_flag |= B_SHAREDBUF;
 
   return (fd2);
-- 
2.40.1