This fixes a regression from commit 36117968ad.
wrapped_url_read() used to be able to return positive number from
ffurl_read(). It relies on the result to check if EOF is reached in
async_buffer_task().
But FIFO callbacks must return 0 on success. This should be handled
in ring_write() instead.
Test case:
ffmpeg -f lavfi -i testsrc -t 1 test.mp4
ffmpeg -i async:test.mp4
Signed-off-by: Guangyu Sun <gsun@roblox.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>