The right of contribution exists among joint tort-feasors. A joint tort-feasor is not entitled to a money judgment for contribution until the joint tort-feasor has by payment discharged the common liability or has paid more than a pro rata share of the common liability. A joint tort-feasor who enters into a settlement with the injured person is not entitled to recover contribution from another joint tort-feasor whose liability to the injured person is not extinguished by the settlement.