Fix PHP 7.3 compatibility in \wcf\util\Diff
Fix PHP 7.3 compatibility in \wcf\util\Diff

The previous code worked correctly by accident: As the `switch` is the
last statement in the `for`-loop `continue`ing the `switch` is equivalent
to `continue`ing the `for`-loop.

Cyperghost/WCF,Cyperghost/WCF,WoltLab/WCF,SoftCreatR/WCF,SoftCreatR/WCF,WoltLab/WCF,Cyperghost/WCF,MenesesEvandro/WCF,MenesesEvandro/WCF,WoltLab/WCF,WoltLab/WCF,SoftCreatR/WCF,Cyperghost/WCF,SoftCreatR/WCF,Cyperghost/WCF