Fix SSG fallback with basepath

[jvarho]

Fixes #990

There were two issues:

1. Page requests happened with basePath in s3Origin.path while data requests had it in request.uri, so normalizeUri broke with fallback pages.
2. Since basePath starts with / all the S3 operations from response handler broke when using basePath.

[codecov]

Codecov Report

Merging #992 (108bdb6) into master (72b3c69) will increase coverage by 0.10%.
The diff coverage is 100.00%.

❗ Current head 108bdb6 differs from pull request most recent head 7d385b5. Consider uploading reports for the commit 7d385b5 to get more accurate results

@@            Coverage Diff             @@
##           master     #992      +/-   ##
==========================================
+ Coverage   81.51%   81.61%   +0.10%     
==========================================
  Files          69       69              
  Lines        2537     2540       +3     
  Branches      604      602       -2     
==========================================
+ Hits         2068     2073       +5     
  Misses        402      402              
+ Partials       67       65       -2     

Impacted Files	Coverage Δ
...ackages/libs/lambda-at-edge/src/default-handler.ts	94.29% <100.00%> (+0.73%)	⬆️

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[dphang]

Thanks, I thought these cases covered in the e2e tests but maybe the fallback tests are not working correctly, might be worth trying to take a look at those if you have time too.

Let me run the e2e tests and see if something needs fixing there. (link: https://github.com/serverless-nextjs/serverless-next.js/actions/runs/749314587)

[jvarho]

I don't think any of the e2e tests combine base path and dynamic paths.

I was going to look into implementing fallback: blocking when I have the time, but it might be worthwhile to write some more tests and refactor the handler first.

[dphang]

I don't think any of the e2e tests combine base path and dynamic paths.

I was going to look into implementing fallback: blocking when I have the time, but it might be worthwhile to write some more tests and refactor the handler first.

Makes sense, yea we have a separate test package for more dynamic pages tests but that was just without the basepath. Maybe we can just add the test to the next-app-with-basepath package