gst/avi/gstavidemux.c: Error out properly when pull_range fails while we're reading the headers, instead of just paus...

Original commit message from CVS:
* gst/avi/gstavidemux.c: (gst_avi_demux_stream_header_pull):
Error out properly when pull_range fails while we're reading the
headers, instead of just pausing the task silently. Fixes #399338.