Bug: stats.lua can return lastYear = 491972

The URL https://lists.apache.org/api/stats.lua?list=dev&domain=lucene.apache.org&d=1970-01
is currently returning the following:

{"lastYear":491972,"no_threads":0,"took":7334,"thread_struct":{},"list":"dev@lucene.apache.org","unixtime":1473894371,"hits":0,"participants":{},"emails":{},"debug":[39,32,1,24,7198,7,2,24],"max":15000,"domain":"lucene.apache.org","name":"dev","searchlist":"","firstYear":2001,"using_wc":false,"numparts":0}

This is clearly wrong

[Note: I used the d qualifier to reduce the output]

Reproduce the response from the stats.lua API URL using the d=1970-01 qualifier and inspect how that endpoint computes lastYear. Compare the result with the returned firstYear and requested date; done means the endpoint no longer returns the incorrect 491972 value.

Written by the indexing model from the issue text.