go/doc: avoid panic on references to functions with no body
This change guards a call to ast.Inspect with a nil check on the first
argument. This avoids a panic when inspecting a reference to a function
with a nil body. This can only happen when a function body is defined outside Go.
Fixes #42706
Change-Id: I91bc607b24b6224920c24cfd07e76ce7737a98d4
GitHub-Last-Rev:
08072b9ce5c1fd4ee77eba6f1acc0a84e838ad7b
GitHub-Pull-Request: golang/go#43011
Reviewed-on: https://go-review.googlesource.com/c/go/+/275516
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Trust: Daniel Martí <mvdan@mvdan.cc>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>