cmd/doc: show the package clause always
If no writes to the package buffer happen, then the package clause
does not get printed. This is a bug for cases where a file just contains
the package clause.
We fix this by separating the printing of package clause to a new
function and calling it from (*pkgBuffer).Write as well as (*Package).flush.
Updates #31457
Change-Id: Ia3bd0ea3963274c460a45d1e37fafc6ee0a197f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/206128
Run-TryBot: Agniva De Sarker <agniva.quicksilver@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>