erc20, rewardPerBlock, endBlock and startBlock are set in the constructor and can’t be modified later. The arguments passed are not checked if they are valid and non-zero. Also, contract can be funded only when block.number < endBlock. So, if startBlock is set to block.number, then contract won't be funded and will be useless. Also, it needs to be ensured that startBlock is not too much in the future otherwise contract will be open for funding but reward distribution will start too long in the future.

Add basic sanitization for input value considering above cases.