Shouldn't ignore (pre)endorsements of current round if proposal not already received

In case messages reception may be arbitrary reordered, we may have slow convergence for a level (or maybe a progress issue, in the sense that we'll be stuck at the same level).

This is possible because (pre)endorsements of current round are ignored if the corresponding proposal is not already received.

This issue is likely not present in Tezos' code because when the baker receives a new head, it (re)fetchs all the operations from the mempool (in which (pre)endorsements that arrived too earlier are kept).