Comment 7 for bug 358223

the valgrind error

==17206== Invalid read of size 1
==17206== at 0x4A0A034: strlen (mc_replace_strmem.c:242)
==17206== by 0x3A19C4975D: vfprintf (in /lib/libc-2.9.so)
==17206== by 0x3A19CFED7F: __vasprintf_chk (in /lib/libc-2.9.so)
==17206== by 0x3A1B86F34A: g_vasprintf (in /usr/lib/libglib-2.0.so.0.2000.0)
==17206== by 0x3A1B85CB6D: g_string_append_vprintf (in /usr/lib/libglib-2.0.so.0.2000.0)
==17206== by 0x3A1B85CC87: g_string_append_printf (in /usr/lib/libglib-2.0.so.0.2000.0)
==17206== by 0x913977C: em_format_describe_part (em-format.c:1167)
==17206== by 0x91335A4: efhd_format_attachment (em-format-html-display.c:2502)
==17206== by 0x913A8ED: em_format_part_as (em-format.c:634)
==17206== by 0x913AA61: em_format_part (em-format.c:653)
==17206== by 0x913B38B: emf_multipart_mixed (em-format.c:1259)
==17206== by 0x913A98F: em_format_part_as (em-format.c:626)
==17206== by 0x913AA61: em_format_part (em-format.c:653)
==17206== by 0x9136EEB: efh_format_message (em-format-html.c:2088)
==17206== by 0x9135C4F: efh_format_exec (em-format-html.c:1274)
==17206== by 0x915BA39: mail_msg_proxy (mail-mt.c:520)
==17206== by 0x3A1B864EB6: (within /usr/lib/libglib-2.0.so.0.2000.0)
==17206== by 0x3A1B863953: (within /usr/lib/libglib-2.0.so.0.2000.0)
==17206== by 0x3A1A8073B9: start_thread (in /lib/libpthread-2.9.so)
==17206== by 0x3A19CE5FCC: clone (in /lib/libc-2.9.so)
==17206== Address 0x8aae999 is not stack'd, malloc'd or (recently) free'd