fix(apiform): encode typed nil readers as empty fields instead of panicking

[Hughhhhcoder]

Problem

encodeValue routes any value whose type implements io.Reader into encodeReader before checking whether the value is a typed nil. A typed nil pointer (or nil interface) whose type implements io.Reader therefore reaches encodeReader, which calls io.Copy on a nil receiver and panics.

Fix

Move the nil check for reflect.Pointer and reflect.Interface ahead of the io.Reader interface check, so typed nil values are encoded as empty fields instead of panicking.

Test

Added a regression test in internal/apiform/form_test.go covering typed nil io.Reader values. go test ./internal/apiform/... passes.

[Hughhhhcoder]

The latest pull-request workflow runs (CI, CodeQL, and Castiron custom code) are completed with action_required. Could a maintainer approve the workflows so they can run? This appears to be a workflow-permission gate rather than a code failure; the focused and package tests pass locally.

[jbeckwith-oai]

Thanks for the contribution. This duplicates #89 and the earlier PR #90, which already owns the original report. While reviewing both, I found that the shallow nil check still panicked when a typed-nil pointer was wrapped in an io.Reader-typed map or slice. I have pushed the interface-unwrapping correction and expanded regression coverage to #90, so I am closing this PR in favor of that one.