山本です。

とりあえず以下のような感じで修正しようと思います。
(あんまりスマートじゃないですが…)

--- src/procheader.c    23 Apr 2003 05:39:14 -0000      1.26
+++ src/procheader.c    29 Jun 2004 09:03:28 -0000
@@ -1,6 +1,6 @@
 /*
  * Sylpheed -- a GTK+ based, lightweight, and fast e-mail client
- * Copyright (C) 1999-2003 Hiroyuki Yamamoto
+ * Copyright (C) 1999-2004 Hiroyuki Yamamoto
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -84,17 +84,18 @@
                        else if (nexthead == EOF)
                                break;
                        else if (folded == TRUE) {
+                               if ((len - (bufp - buf)) <= 2) break;
+
                                if (nexthead == '\r' || nexthead == '\n') {
-                                       folded = FALSE;
-                                       continue;
+                                       ungetc(nexthead, fp);
+                                       nexthead = '\0';
                                }
 
-                               if ((len - (bufp - buf)) <= 2) break;
-
                                /* replace return code on the tail end
                                   with space */
                                *bufp++ = ' ';
-                               *bufp++ = nexthead;
+                               if (nexthead)
+                                       *bufp++ = nexthead;
                                *bufp = '\0';
                                /* concatenate next line */
                                if (fgets(bufp, len - (bufp - buf), fp)
@@ -169,17 +170,18 @@
                else if (nexthead == EOF)
                        break;
                else if (folded == TRUE) {
+                       if ((len - (bufp - buf)) <= 2) break;
+
                        if (nexthead == '\r' || nexthead == '\n') {
-                               folded = FALSE;
-                               continue;
+                               ungetc(nexthead, fp);
+                               nexthead = '\0';
                        }
 
-                       if ((len - (bufp - buf)) <= 2) break;
-
                        /* replace return code on the tail end
                           with space */
                        *bufp++ = ' ';
-                       *bufp++ = nexthead;
+                       if (nexthead)
+                               *bufp++ = nexthead;
                        *bufp = '\0';


-- 
Hiroyuki Yamamoto <hiro-y@xxxxxxxxxx>
http://www.kcn.ne.jp/~hiro-y/index.cgi
http://sylpheed.good-day.net/ (Sylpheed)