aiff: Fix infinite loop in header parsing.
gst_aiff_parse_ignore_chunk() can fail if not enough data is in the adapter yet. In current code, this will cause gst_aiff_parse_stream_headers() to loop forever, since the failure is ignored with no exit condition set.
This behaviour was observed with an AIFF file with a large APPL chunk in the header.
The fix is to return GST_FLOW_OK when we don't have enough data yet to flush the adapter so GstPadChainFunction have a chance to retrieve more data.