Refresh seeks are automatically issued when changing filters, which
improves user experience if these filters change buffering or such.
The refresh seek could actually overwrite a previously ongoing seek:
set pause yes
set time-pos 10
set vf ""
Here, the video code issued a refresh seek to the previous video
position, which could be different from the previously triggered (and
still ongoing) seek, this overwriting the seek.
Factor all refresh seek handling into a new function, and make it handle
ongoing seeks correctly.
Remove the weird new canonical_pts field, which actually had no use.
Fixes#4757.
68201f4591