Issue 3254 protobuf null pointer exceptions

[kwvanderlinde]

Identify the Bug or Feature request

Improves #3254

Description of the Change

There are several model types that have fields that aren't expected to be null but which can be made null as a result of deserialization. This made it impossible to open many campaign files, possibly also affecting other actions that require deserialization. This changes primarly adds or modifies readResolve() methods for various model types to avoid undesirable nulls.

A couple smaller fixes are also included:

• Infinite recursion for parameterless token updates.
• Fix for tokens marked Visible to players also becoming Visible over FoW when a server is started.
• Handle null exposed area GUIDs by ignoring them while serializing.

Possible Drawbacks

Shouldn't be any drawbacks in behaviour. There may be a better way to handle deserialization with missing / null fields that could avoid some of these checks.

Skipping the null keys for Zone.exposedAreaMeta is kind of the wildcard in this change. Those keys shouldn't be possible and yet they exist, so maybe there could be some edge case where they can be read back out again.

Documentation Notes

N/A

Release Notes

N/A

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This change is 

[Phergus]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @kwvanderlinde)

[kwvanderlinde]

Fixed the formatting - sorry about that.

[Phergus]

We've all done it.

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @kwvanderlinde)