rtpstats: fix assertion 'denom > 0' failed
rtpstats: fix assertion 'denom > 0' failed

gst_util_uint64_scale_int takes a gint as denom parameter
whereas ctx->clock_rate is a guint32.

It happens when gst_rtp_packet_rate_ctx_reset set clock_rate
to -1.

So just define clock_rate as gint like it is done in rtpsource.h

https://bugzilla.gnome.org/show_bug.cgi?id=784250

stfl/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good