Added 'early returns'.

According to:
<sanderd17>Btw, early returns: In StatisticsTracker, there are at least two cases where you didn't chose for early returns: L217 and L230. If you just check for the negative, you don't need all that indentation
<sanderd17>L165 and L193 too

Signed-off-by: Grzes <kabza.grzegorz@gmail.com>