Investigate & fix proposal validation- unauthorized error

[MrDarthShoe]

clippy-complexity lints indicated that in common.rs unauthorized error is never returned. This is probably bug which needs proper investigation and probably fix with test

[pwalski]

The question if this conditional block is effectively a dead code is exactly a kind of question for which tools aggregating coverage reports from UT and FT can give answer (this case reminded me today's discussion).

[evik42]

Rafal: probably add return to /core/market/src/negotiation/common.rs#L693