Don't crash with invalid argument in check-coding-systems-region

* src/coding.c (Fcheck_coding_systems_region): Don't crash if
the third arg contains something that isn't a coding system.
* test/src/coding-tests.el (coding-check-coding-systems-region):
New test.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/coding.c b/src/coding.c
index c24c70c0899..ffcb9cf0a1a 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -9302,7 +9302,10 @@ is nil.  */)
   for (tail = coding_system_list; CONSP (tail); tail = XCDR (tail))
     {
       elt = XCAR (tail);
-      attrs = AREF (CODING_SYSTEM_SPEC (elt), 0);
+      Lisp_Object spec = CODING_SYSTEM_SPEC (elt);
+      if (!VECTORP (spec))
+        xsignal1 (Qcoding_system_error, elt);
+      attrs = AREF (spec, 0);
       ASET (attrs, coding_attr_trans_tbl,
             get_translation_table (attrs, 1, NULL));
       list = Fcons (list2 (elt, attrs), list);