Handle post_init and unknown terminate crash

Proposed Changes

Noticed that if a crash happens in the init callback in a ra_machine, the actual error gets obfuscated by the ra_server_proc not handling a terminate without a state record.

Types of Changes

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[x] Bug fix (non-breaking change which fixes issue #NNNN)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Documentation (correction or otherwise)
[ ] Cosmetics (whitespace, appearance)

Checklist

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[x] I have read the CONTRIBUTING.md document
[x] I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
[x] All tests pass locally with my changes
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have added necessary documentation (if appropriate)
[x] Any dependent changes have been merged and published in related repositories

Further Comments

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rabbitmq / ra