preproc: Don't dereference nil @istk

If not input was specified istk = NULL, so don't dereference it.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/preproc.c b/preproc.c
index 0c9bf2d3..9dc3d88d 100644
--- a/preproc.c
+++ b/preproc.c
@@ -5277,7 +5277,8 @@ static void pp_error_list_macros(int severity)
     severity |= ERR_PP_LISTMACRO | ERR_NO_SEVERITY;
     src_get(&saved_line, &saved_fname);
 
-    pp_list_one_macro(istk->mstk, severity);
+    if (istk)
+        pp_list_one_macro(istk->mstk, severity);
 
     src_set(saved_line, saved_fname);
 }