interlace: Fix a double-unref on shutdown
Trying to reset before the pads have been deactivated races with the
streaming thread. There was also a buggy buffer clear leaving a dangling
stored_frame
pointer around. Use gst_interlace_reset
so this happens
properly.
As requested in gstreamer!1039 (comment 1113485).
Edited by Tim-Philipp Müller