bug#10536: 23.3; Make base64-decode more fault tolerant

[Wolfram Gloger]

Hello,

Not a bug in Emacs, but I have received base64-encoded mails from a
not-so-small company which could not be decoded.  It turns out that
there was a missing padding character, i.e. the last quartet was
"xy=" rather than the proper "xy==".

I would suggest that base64-decode should tolerate this, like with
the appended patch.

Regards,
Wolfram.

--- src/fns.c~  2011-04-05 05:46:44.000000000 +0200
+++ src/fns.c   2012-01-17 13:59:26.000000000 +0100
@@ -3590,7 +3590,8 @@
 
       if (c == '=')
        {
-         READ_QUADRUPLET_BYTE (-1);
+         /* Be tolerant against missing final padding '='.  */
+         READ_QUADRUPLET_BYTE (e-to);
 
          if (c != '=')
            return -1;