linkchecker misreports target of broken link fragment

[jsha]

Steps to reproduce:

mkdir /tmp/links
cat <<EOF > /tmp/links/a.html
<div id="something">
  <a href="#something">
  <a href="b.html#something">
</div>
EOF
cat <<EOF > /tmp/links/b.html
<div id="else">
  <a href="#else">
</div>
EOF

./build/x86_64-unknown-linux-gnu/stage0-tools-bin/linkchecker /tmp/links/

Expected output:

a.html:3: broken link fragment #somethingpointing tob.html``

Actual output:

a.html:3: broken link fragment #somethingpointing toa.html``

(the difference: "pointing to a.html" vs "pointing to b.html")

This problem manifests specifically when a given file has an anchor with the same name as an anchor in a different file, and the anchor in the other file is missing.

I ran into this in practice #85970 and it sent me in a wrong debugging direction for a little while.

[ehuss]

Ah, sorry about that, I'll post a quick fix.