Walletwasabi: Look for consecutive unused addresses (gap limit)

[yahiheb]

1. Go to receive tab
2. Generate 11 new addresses
3. Send bitcoin to the 11th address (now there is 10 consecutive unused addresses)
4. Generate 12 more new addresses (now there is 22 unused addresses in receive tab)
5. Send bitcoin to the last generated address (now there is 21 unused addresses but only 11 consecutive unused addresses)
6. Wait for the transactions to get confirmed then close Wasabi
7. Open Wasabi, go to recover wallet, change the minimum gap limit to 21 and recover your wallet

When the wallet finishes loading you will see only one coin instead of two.

This is because when recovering a wallet Wasabi uses the minimum gap limit in order to stop looking for addresses if there are that many unused addresses, but it doesn't take into consideration that the unused addresses should be consecutive.

[lontivero]

Yes, that's true and you are right. Would you like to take this one? I think you should check that the number of consecutive keys are filled. Try with something like this:

```c#
// KeyManager.cs file

var keys = GetKeys(KeyState.Clean, true);
var consecutives = keys.Skip(1).Zip(keys, (curr, prev) => curr.Index == prev.Index + 1).Count(x=>x);

while (consecutives < MinGapLimit)
{
// generate one more
}
```

[MaxHillebrand]

Yes, good catch!

[yahiheb]

Would you like to take this one?

Yes I will try.

[lontivero]

Sorry @yahiheb, I did some progress with this issue because i think it is rather important. Please, review my PR and repeat your test with it. If you find a better solution just push it on top.