gst-libs/gst/riff/riff-read.c: Don't touch events after not owning them anymore.

gst-libs/gst/riff/riff-read.c: Don't touch events after not owning them anymore.

Original commit message from CVS:
* gst-libs/gst/riff/riff-read.c: (gst_riff_read_seek):
Don't touch events after not owning them anymore.
* gst/wavparse/gstwavparse.c: (gst_wavparse_base_init),
(gst_wavparse_fmt), (gst_wavparse_other),
(gst_wavparse_handle_seek), (gst_wavparse_loop),
(gst_wavparse_pad_convert), (gst_wavparse_pad_query),
(gst_wavparse_srcpad_event):
* gst/wavparse/gstwavparse.h:
Add seeking, fix querying.