add black to play behavior to task_preview_tile

[Cidragon]

fix #195

The code only does 2 simple things:

• It remove and if/else statement to just make it an if by using taskData variable as a starting point to check if the snapshot data is null or not.
• set task value depending if the settings include always black to play.

[ale64bit]

can't we simplify this condition?

final task = context.settings.alwaysBlackToPlay 
              ? taskData.withBlackToPlay()
              : taskData;

[Cidragon]

yes, the function withBlackToPlay does check if the first to move is black to play so it's not necessary to check it previously.

I can remove the second condition if you want, the only problem is that i don't know what should I do now that the pull request doesn't follow the main branch anymore. do I need to sync first and then commit later?