I found what could be a bug in wavparse or riff-read when using it
though. When downloading this file, I stopped the download before it
completed, but tried to play the file.
gst-launch then complains about trying to push a NULL buffer. 
After gdb-ing a bit, I found that wavparse calls
gst_riff_read_element_data asking it to read XXX bytes, this function
can't read that many bytes so it returns NULL and then wavparse pushes
that NULL. It probably happens when reaching the end of my truncated
file even though I didn't check.
I was wondering if it was intentional that gst_riff_read_element_data
basically does:
if ((got = gst_bytestream_peek (riff->bs, &buf, length)) != length) {
        return NULL;
}
return buf;

or if it should be more clever? (for example, return buffers whose
length is smaller than the length asked to the function, or try a bit
harder to get a full buffer).