cmd/doc: allow go doc -http without package in current directory
go doc tries to find a package to display documentation for. In the case
that no package is provided, it uses "." just like go list does. So if
go doc -http is run without any arguments, it tries to show the
documentation for the package in the current directory. As a special
case, if no arguments are provided, allow no package to match the
current directory and just open the root pkgsite page.
For #68106
Change-Id: I6d65b160a838591db953fac630eced6b09106877
Reviewed-on: https://go-review.googlesource.com/c/go/+/675075 Reviewed-by: Alan Donovan <adonovan@google.com> Reviewed-by: Michael Matloob <matloob@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>