TokenNetworkRegistry proxy should check settlement_timeout_min is not zero

[pirapira]

Smart contract proxies should try to avoid sending transactions that are going to fail. Currently, TokenNetworkRegistry's proxy sends createERC20TokenNetwork() transactions without checking the value of settlement_timeout_min. If settlement_timeout_min is zero, the transaction fails because TokenNetwork's constructor fails.

Also, when a transaction fails in a block or when gas estimation fails, a similar check helps to diagnose the problem.

This issue keeps track of adding these checks in TokenNetworkRegistry's proxy.

[pirapira]

This is a part of #4792

[rakanalh]

As i wrote in one of the issues you created, settlement_timeout_min and settlement_timeout_max are checked in the contract's constructor. No "precondition" check should take place in the proxy methods for require/asserts that are executed in the contract's constructor.

Edit: I was wrong on this one. The TokenNetwork constructor is being called here:

https://github.com/raiden-network/raiden-contracts/blob/94f1428d2fad4719efffb26be3d7731d7bb3f3da/raiden_contracts/data/source/raiden/TokenNetworkRegistry.sol#L87

So those checks should be there.