Fixed handling for offer operation updates.
Fixed handling for offer operation updates.

The handling of offer operation updates introduced in `c946615ec6d`
made use of an update's `latest_status` without making sure that any
value was set. This could lead to situation where an uninitialized
enum value was switched on which would have caused a fatal error at
runtime.

This patch replaces uses of `latest_status` with `state` which does
contain the information we care about. We also adjust the error
logging so we log the value that lead to the error, not some other
value.

Review: https://reviews.apache.org/r/69157/

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