gst-libs/gst/audio/gstringbuffer.c: Check arguments passed to public functions instea...

gst-libs/gst/audio/gstringbuffer.c: Check arguments passed to public functions instead of crashing.

Original commit message from CVS:
* gst-libs/gst/audio/gstringbuffer.c:
(gst_ring_buffer_set_callback), (gst_ring_buffer_acquire),
(gst_ring_buffer_release), (gst_ring_buffer_is_acquired),
(gst_ring_buffer_set_flushing), (gst_ring_buffer_start),
(gst_ring_buffer_pause), (gst_ring_buffer_stop),
(gst_ring_buffer_delay), (gst_ring_buffer_samples_done),
(gst_ring_buffer_set_sample), (gst_ring_buffer_clear_all),
(gst_ring_buffer_commit), (gst_ring_buffer_read),
(gst_ring_buffer_prepare_read), (gst_ring_buffer_advance),
(gst_ring_buffer_clear), (gst_ring_buffer_may_start):
Check arguments passed to public functions instead of
crashing.