BUG: Previous button not work properly in shuffle mode

[happyuser]

Button Previous in playlist does not move to the previous played movie when "Shuffle" is active, it actually goes Random and there is no way to go back to the item in playlist that was playing.
The Previous and Next buttons are actually doing the same - start random item from playlist.
Maybe it's considered to be acceptable but actually is a bug, no proper players do like that with playlist. As SMPlayer is the best player, so it should be proper in this way too.

How to reproduce:
1) Activate Shuffle in playlist.
2) Play media A and then media B in playlist.
3) Press button Previous in playlist when media B is still playing.

What happens:
SMPlayer plays some random media

What is expected:
SMPlayer plays media A.

NOTE: this issue can be fixed not only in a direct-fix way but also by reorganizing Shuffle mode that I will provide as a separate feature request.