default initialize source_timeout with -1 so we have a sane timeout value

default initialize source_timeout with -1 so we have a sane timeout value

Mon Dec 21 03:48:04 1998  Tim Janik  <timj@gtk.org>

        * gmain.c (g_main_iterate): default initialize source_timeout with -1
        so we have a sane timeout value if (*prpare) doesn't set it.