TokenNetworkRegistry's add_token() should check if secret_registry_address is zero

[pirapira]

If the given secret_registry_address is zero, the transaction will fail, so the proxy should raise BrokenPreconditionError.

This is a part of #4792

[rakanalh]

According to the contracts:

https://github.com/raiden-network/raiden-contracts/blob/94f1428d2fad4719efffb26be3d7731d7bb3f3da/raiden_contracts/data/source/raiden/TokenNetworkRegistry.sol#L70-L105

There is no require/assert for the secret registry address when createERC20TokenNetwork is called.

The assert exists in the constructor of the contract which means that if that fails there would be no usable instance of the contracts.

[pirapira]

@rakanalh createERC20TokenNetwork() calls the constructor of TokenNetwork. The constructor of TokenNetwork contains a require(secret_registry_address != 0);.

[pirapira]

I assigned myself because @rakanalh has not understood why the change has to be made.

[rakanalh]

@pirapira my PR will handle this one as well.