NPE triggered if server receives a vote for a server id not in their voting view

We've observed the following behavior in elections when a node is lagging behind the quorum in its view of the ensemble topology.

• Node A is operating with node B in its voting view, but without view of node C.

• B votes for C.

• A then switches its vote to C, but throws a NPE when attempting to connect.

This causes the QuorumPeer to spin up a Follower only to immediately have it shutdown by the exception.

Ideally, A would not advertise a vote for a server that it will not follow.