Resolve "Do a better job of logging when fetches-per-zone is triggered"

When initially hitting the fetches-per-zone value, a log message is being generated for the event of dropping the first fetch, then any further log events occur only when another fetch is being dropped and 60 seconds have been passed since the last logged message.

That logic isn't ideal because when the counter of the outstanding fetches reaches zero, the structure holding the counters' values will get deleted, and the information about the dropped fetches accumulated during the last minute will not be logged.

Improve the fcount_logspill() function to make sure that the final values are getting logged before the counter object gets destroyed.

Closes #3461 (closed)