if we were unable to initialize the tabe autoinc value. This is required for
the open to succeed. The only condition we currently treat as a hard error
is if the autoinc field instance passed in by MySQL is NULL.

Previously if the table autoinc value was 0 and the next value was requested
we had an assertion that would fail. Change that assertion and treat a value
of 0 to mean that the autoinc system is unavailable. Generation of next
value will now return failure.

rb://237