TokenNetworkRegistry proxy should check that token_address is nonzero

[pirapira]

This condition should be checked in

• the precondition checks before the gas estimation (if the condition is unmet, BrokenPreconditionError should be thrown)
• the callers of the proxy.

Since the condition is not affected by the chain state, the check doesn't need to be repeated in the post-failure checks.

This is a part of #4792.