libs: encoder: set framerate if bigger than 0/1
libs: encoder: set framerate if bigger than 0/1

Just set the framerate parameter if the framerate numerator and
denominator are bigger than zero.

Otherwise, in Intel Gen6 driver, a warning is raised disabling the
bitrate control.

Original-patch-by: Hyunjun Ko <zzoon@igalia.com>

https://bugzilla.gnome.org/show_bug.cgi?id=783532

GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi