Created attachment 1375 [details]
Patch to fix memory corruption in sc_html_read_line()

The attached patch fixes crashes like this:

(gdb) r
Starting program: /usr/local/bin/claws-mail 
[New LWP 101445]
[New Thread 80b006400 (LWP 101445)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 80b006400 (LWP 101445)]
0x00000000004c1c71 in sc_html_read_line (parser=0x80b1dda00) at html.c:466
466		index = parser->bufp - parser->buf->str;
(gdb) p *parser
$1 = {fp = 0x80b14d5e0, conv = 0x8056e1f50, symbol_table = 0x8056e1f00 <g_idle_funcs>, alt_symbol_table = 0x1, str = 0x80b0546c0, buf = 0x10000006c, bufp = 0x1f5 <Address 0x1f5 out of bounds>, 
  state = SC_HTML_NORMAL, href = 0x0, newline = 0, empty_line = 0, space = 0, pre = 0}
(gdb) where
#0  0x00000000004c1c71 in sc_html_read_line (parser=0x80b1dda00) at html.c:466
#1  0x00000000004c1960 in sc_html_parse (parser=0x80b1ddac0) at html.c:395
#2  0x00000000005e538a in textview_show_html (textview=0x80b19dcc0, fp=0x806feb580, conv=0x80b14d5c0) at textview.c:1214
#3  0x00000000005e26f8 in textview_write_body (textview=0x80b19dcc0, mimeinfo=0x80b08a780) at textview.c:1067
[...]

Note that parser's last byte got overwritten in #0.