vasnwprintf: Fix crash upon conversion failure when processing %s

[Bruno Haible]

This patch fixes a crash (abort) during the %s processing in vasnwprintf.


2023-03-31  Bruno Haible  <bruno@clisp.org>

        vasnwprintf: Fix crash upon conversion failure when processing %s.
        * lib/vasnprintf.c (VASNPRINTF): When processing %s with !has_precision
        and !has_width, don't call abort() if there is a conversion failure.

diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
index 83128fd1ea..8ffab85995 100644
--- a/lib/vasnprintf.c
+++ b/lib/vasnprintf.c
@@ -3099,10 +3099,12 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
 #  else
                           count = mbtowc (&wc, arg, arg_end - arg);
 #  endif
-                          if (count <= 0)
-                            /* mbrtowc not consistent with mbrlen, or mbtowc
-                               not consistent with mblen.  */
+                          if (count == 0)
+                            /* mbrtowc not consistent with strlen.  */
                             abort ();
+                          if (count < 0)
+                            /* Invalid or incomplete multibyte character.  */
+                            goto fail_with_EILSEQ;
                           ENSURE_ALLOCATION (xsum (length, 1));
                           result[length++] = wc;
                           arg += count;