Fix dialog InvalidOperationException

[duydang2311]

This PR should close #433. I have changed the response handler from SetResult to TrySetResult to make it safe from the task already completed exception.
However, a better fix might be to not let the response handler executes the second time by destroying the VisibleDialog component when the player responds or disconnects. There are two related callbacks: OnPlayerDisconnect and OnPlayerDialogResponse. But I'm not sure about the execution order of these two callbacks.

[ikkentim]

However, a better fix might be to not let the response handler executes the second time by destroying the VisibleDialog component when the player responds or disconnects. There are two related callbacks: OnPlayerDisconnect and OnPlayerDialogResponse. But I'm not sure about the execution order of these two callbacks.

It might be a good idea to try this out. To try that, edit the OnPlayerDisconnect event handler and destroy the component there, after it is being handled. player.Destroy();

https://github.com/ikkentim/SampSharp/blob/master/src/SampSharp.Entities/SAMP/Dialogs/DialogSystem.cs#L27

[duydang2311]

I also think it's better to do that. OnPlayerDisconnect event handler now should destroy the VisibleDialog component too.

[ikkentim]

Thank you!