[PATCH] adjust_shell_level: check for SHLVL bind failure

[Grisha Levit]

$ bash -c 'unset X; declare -n SHLVL=X[-1]; /'
...
SUMMARY: AddressSanitizer: SEGV variables.c:892 in adjust_shell_level
---
 variables.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/variables.c b/variables.c
index dc74855b..1f9b32c3 100644
--- a/variables.c
+++ b/variables.c
@@ -889,7 +889,8 @@ adjust_shell_level (int change)
     }
 
   temp_var = bind_variable ("SHLVL", new_level, 0);
-  set_auto_export (temp_var);
+  if (temp_var)
+    set_auto_export (temp_var);
 }
 
 static void
-- 
2.54.0