Remove assumption that all Addresses of client are present in Params.Participants

[sophia1ch]

Location

channel/proposal.go

Problem

At completeCPP(...) the code returns an index error if params.Parts[partIdx] does not contain all backend addresses, that are registered as wallet addresses in the client. This means if we want to use one client supporting all backends, if one backend is not compatible yet for cross-contract channels, we cannot use that backend on it's own because we always need to list all participant addresses in Params.

Proposal

Only iterate through the params.Parts to unlock the wallets instead of iterating through c.wallet.