check constructor parameters length

[davidp94]

dp2pDocProof/contracts/MultiSigDocumentSigner.sol

Line 50 in 8be3e18

require(minSignature > 0 && minSignature <= _authorities.length);

Somebody could put the contract in a non working state by specifying an address multiple times and gives a greater number of minRequiredSignature than actual address

the minRequiredSignature should be computed after the loop by summing all unique authorities addresses.