Race condition: lyrics and extra song info appear on other songs when fast skipping

[NyaomiDEV]

Currently, for each update that Sunamu gets, a callback function updateInfo is called with the current update as its argument. This function runs asynchronously and it does a chain of asynchronous stuff:

• update the shown information once, right after the update was pushed (first point of suspension)
• gather more information about the track being played (lyrics.. etc) (second point of suspension)
• update the shown information again, to push all the remaining information to the renderer process(es) (third point of suspension)

Now, if updates were sparse in time, this would've been a non-issue since there'd be plenty of time for the neat completion of any and all of those function calls; however, if a person skips really fast or if they have a bad Internet connection that delays the information gathering, then we are presented with race conditions.

We must avoid those race conditions, and mark as "out of date" all the updateInfo calls running, except the very last one

[NyaomiDEV]

Probably fixed by 700a263