pywb returns status code 200 when archive url not found

[GilHoggarth]

For example, https://webarchive.org.uk/wayback/archive/2019/www.coinbase.com
In the wa-www nginx log, this request is recorded as a status code 200 whereas the on-screen message is "Url Not Found
The url http://www.coinbase.com/ could not be found in this collection. ".

[ikreymer]

The inner frame response, https://www.webarchive.org.uk/wayback/archive/2019mp_/http://www.coinbase.com/ is a 404, but not the outer frame, which is always a 200.
The reason is that the lookup does not happen until the inner frame is loaded, to avoid a double query and load the outer frame quickly, but maybe there's a way to improve this..

[anjackson]

Related somewhat to #44. Note that the TimeGate URL (https://beta.webarchive.org.uk/wayback/archive/http://www.coinbase.com/) does the right thing.

[anjackson]

I'm going to call this ticket a duplicate of #44, having clarified that this is part of that issue.