* Make copies of buffers
Avoid reusing one of the incoming arrays as a append extension, and
make a copy of the data. It's cleaner in the long run and possibly
easier for the GC to maintain.
* Avoid appendAssign problems in tag code
Reuse the existing slice when appending.
* Fix appendAssign in encoder_scene_preview_chunk
Appending and creating a new slice is somewhat unintuitive since the
underlying slice might be extended to satisfy the new capacity. This
sometimes leads to faulty logic.
Rewrite the code so it reuses `args` for all appending, and builds one
array clearly in the code. It follows the general style of the function
where `args` is being built in small incremental batches and avoids
the introduction of new names.
* Enable the appendAssign check
This makes us pass all gocritic warnings.
Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>
* Added preview generation fallback feature.
When a preview generation fails (often for wmv/avi files), the new code tries with less stricted (no xerror) and more time consuming options (slow+fast seek).
Fix a minor issue when stash downloads ffmpeg/ffprobe, but doesn't re-detect their paths.
