Fix string-to-multibyte overlong sequence bug

* src/character.h (MULTIBYTE_LENGTH, MULTIBYTE_LENGTH_NO_CHECK):
Remove, replacing with ...
(multibyte_length): ... this new function.  All callers changed.
The new function rejects overlong multibyte forms.
* test/src/buffer-tests.el (buffer-multibyte-overlong-sequences):
New test.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 5398414e6eb..53b3bd960c4 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2634,8 +2634,7 @@ current buffer is cleared.  */)
           if (ASCII_CHAR_P (*p))
             p++, pos++;
           else if (EQ (flag, Qt)
-                   && ! CHAR_BYTE8_HEAD_P (*p)
-                   && (bytes = MULTIBYTE_LENGTH (p, pend)) > 0)
+                   && 0 < (bytes = multibyte_length (p, pend, true, false)))
             p += bytes, pos += bytes;
           else
             {