An identity with its membership which just expires proceed block calculation

Cf: https://forum.duniter.org/t/g1-test-dans-les-choux/4192/316?u=moul

It is not happening when launching pow with an already expired membership identity.

But, it happen, when an member identity is calculating, then loose its membership and keep calculate.

There is no further check at each block if the identity is still member. A mechanism should handle that.