Automatically load the last downloaded subtitle, replacing the previous one

[cipricus]

That is default in VLC and SMPlayer, very useful in order to test the sub (and decide whether to search for another or not) and to not have to select it manually.
Maybe related to #785.

[tomasklaen]

We already load downloaded subtitles with sub-add <file> command, which sets it as current subtitle track by default, and afterwards we ensure sub-visibility yes.

Not sure what else is to be done here, or why it doesn't work for you.

[candrapersada]

auto load subtitle use the same name

Sonic the Hedgehog 2.mp4
Sonic the Hedgehog 2.srt