erl_docgen: Fix generating docs chunk entry for `<seeerl>`
erl_docgen: Fix generating docs chunk entry for `<seeerl>`

Before this patch, this XML:

    <!-- https://github.com/erlang/otp/blob/a40b5380e05a8b390c776556521b6e94e9e11b73/lib/stdlib/doc/src/binary.xml#L472:L474 -->
    are also available in the
    <seeerl marker="erts:erlang"><c>erlang</c></seeerl>
    module under the names

Produced this chunk entry:

    <<" are also available in the ">>,
    {a,[{href,<<"stdlib:binary#erts:erlang">>},
        {rel,<<"https://erlang.org/doc/link/seeerl">>}],
       [{code,[],[<<"erlang">>]}]},
    <<" module under the names ">>,

Note the `stdlib:binary#erts:erlang` instead of the expected
`stdlib:binary`.

With this patch we have the following behaviour. Say, we are generating
docs for the app `myapp` and the module `mymod`:

    "app:mod#anchor" => "app:mod#anchor"
    "mod#anchor"     => "myapp:mod#anchor"
    "app:mod"        => "app:mod"
    "mod"            => "myapp:mod"

getong/otp,getong/otp,vinoski/otp,potatosalad/otp,dgud/otp,erlang/otp,dumbbell/otp,ferd/otp,erlang/otp,isvilen/otp,g-andrade/otp,dgud/otp,vinoski/otp,mikpe/otp,dgud/otp,emacsmirror/erlang,jj1bdx/otp,mikpe/otp,emacsmirror/erlang,dgud/otp,g-andrade/otp,mikpe/otp,dumbbell/otp,jj1bdx/otp,g-andrade/otp,mikpe/otp,potatosalad/otp,rlipscombe/otp,bjorng/otp,emacsmirror/erlang,bjorng/otp,ferd/otp,ferd/otp,rlipscombe/otp,dumbbell/otp,mikpe/otp,g-andrade/otp,jj1bdx/otp,emacsmirror/erlang,emacsmirror/erlang,uabboli/otp,jj1bdx/otp,uabboli/otp,bjorng/otp,g-andrade/otp,vinoski/otp,dumbbell/otp,jj1bdx/otp,ferd/otp,ferd/otp,rlipscombe/otp,uabboli/otp,vinoski/otp,dumbbell/otp,potatosalad/otp,vinoski/otp,dgud/otp,emacsmirror/erlang,erlang/otp,emacsmirror/erlang,isvilen/otp,jj1bdx/otp,uabboli/otp,emacsmirror/erlang,emacsmirror/erlang,bjorng/otp,potatosalad/otp,erlang/otp,potatosalad/otp,isvilen/otp,isvilen/otp,jj1bdx/otp,erlang/otp,dumbbell/otp,getong/otp,jj1bdx/otp,vinoski/otp,isvilen/otp,dgud/otp,potatosalad/otp,getong/otp,mikpe/otp,mikpe/otp,mikpe/otp,uabboli/otp,potatosalad/otp,uabboli/otp,vinoski/otp,rlipscombe/otp,dgud/otp,vinoski/otp,potatosalad/otp,rlipscombe/otp,uabboli/otp,bjorng/otp,g-andrade/otp,ferd/otp,mikpe/otp,ferd/otp,g-andrade/otp,isvilen/otp,erlang/otp,vinoski/otp,potatosalad/otp,mikpe/otp,rlipscombe/otp,uabboli/otp,erlang/otp,dgud/otp,g-andrade/otp,emacsmirror/erlang,dgud/otp,bjorng/otp,g-andrade/otp,dumbbell/otp,rlipscombe/otp,isvilen/otp,ferd/otp,g-andrade/otp,bjorng/otp,erlang/otp,getong/otp,getong/otp,isvilen/otp,dumbbell/otp,getong/otp,ferd/otp,rlipscombe/otp,getong/otp,dumbbell/otp,bjorng/otp,dumbbell/otp,erlang/otp,jj1bdx/otp,vinoski/otp,bjorng/otp,isvilen/otp,rlipscombe/otp,dgud/otp,rlipscombe/otp,getong/otp,potatosalad/otp,jj1bdx/otp,uabboli/otp,bjorng/otp,erlang/otp,getong/otp,isvilen/otp