This also fixes a potential buffer overlow on Windows.
Window _snprintf does not null terminate the string in case
the formatted length is longer than the given buffer size.
http://msdn.microsoft.com/en-us/library/2ts7cx93%28v=vs.110%29.aspx
(mingw's uses _vsnprintf under the hood which is also affected).
Alternatively we could rely in g_snprintf() to truncate the
string.
d0b95b7685