qtdemux: fix framerate calculation for fragmented format

qtdemux: fix framerate calculation for fragmented format

qtdemux calculates framerate using duration and the number of sample.
In case of fragmented mp4 format, however, the number of sample can
be figure out after parsing every moof box. Because qtdemux does not
parse every moof in QTDEMUX_STATE_HEADER state, it will cause incorrect
framerate calculation.

This patch will triger gst_qtdemux_configure_stream() for every new moof.
Then, framerate will be calculated by using duration and n_samples of the moof.

https://bugzilla.gnome.org/show_bug.cgi?id=760774