Fixes: #43598
This was a tricky one to find! Not sure why more people aren't
complaining about this issue, was super annoying in my use case since
links had the wrong URL.
## What?
This issue only occurred when basepath was defined and middleware and
dynamic pages are being used.
Example from the reproduction repo mentioned in the issue tagged:
<img width="686" alt="Screenshot 2023-04-23 at 9 32 55 PM"
src="https://user-images.githubusercontent.com/11258286/233850968-e14f6b49-858b-410e-b8f9-93c90447090a.png">
## Why?
`nextConfig` wasn't passed to `getNextPathnameInfo` function, hence the
basePath wasn't removed from a intermediate variable and that trickled
down to cause this issue.
Added test case based on the issue reproduction repo
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Co-authored-by: Jimmy Lai <laijimmy0@gmail.com>