bug#8601: * 2 -> * 4 typo fix in detect_coding_charset

[Paul Eggert]

By code inspection it appears that there's a typo in
detect_coding_charset: an index is multiplied by 2
when it should be multiplied by 4.  By bisecting it
appears that this typo was introduced here:

        revno: 84043 [merge]
        committer: Miles Bader <miles@gnu.org>
        timestamp: Fri 2008-02-01 16:01:31 +0000
        message:
          Merge unicode branch

          Revision: emacs@sv.gnu.org/emacs--devo--0--patch-1037

so I'll CC: this to Miles.

Here's a proposed patch.  I haven't tested this, as I don't
have the time to fully understand this code.  But from the
description and other uses of code_space, the "* 2" must be
wrong.

=== modified file 'src/coding.c'
--- src/coding.c        2011-04-29 19:47:29 +0000
+++ src/coding.c        2011-05-01 18:05:21 +0000
@@ -5368,8 +5368,8 @@ detect_coding_charset (struct coding_sys
              if (src == src_end)
                goto too_short;
              ONE_MORE_BYTE (c);
-             if (c < charset->code_space[(dim - 1 - idx) * 2]
-                 || c > charset->code_space[(dim - 1 - idx) * 2 + 1])
+             if (c < charset->code_space[(dim - 1 - idx) * 4]
+                 || c > charset->code_space[(dim - 1 - idx) * 4 + 1])
                break;
            }
          if (idx < dim)