gst/flx/gstflxdec.c: If the speed of the file is null in the header, set the frame_time to the default setting of GST...

Original commit message from CVS:
* gst/flx/gstflxdec.c: (gst_flxdec_chain):
If the speed of the file is null in the header, set the frame_time to the default
setting of GST_SECOND / 70. Which is the default frame_delay for .fli files as
stated in this document : http://www.compuphase.com/flic.htm
Would be nice to have the time conversion done properly too
(duration = flxh->frames * flxdec->frame_time)