Anchor link check breaks when target heading comes before the link

[matthandus]

Thank you for the recent improvements on anchor link checks. We noticed that the anchor link check will still return incorrect result and report dead link when the heading that is targeted comes before the anchor link in the document. When the anchor link is above the heading, it passes as expected.

Working sample

Here is an [anchor link](#heading-link-below) sample that passes, as expected.

### Heading link below

Broken sample

### Heading link above

Here is an [anchor link](#heading-link-above) sample that reports as a dead link.

[dklimpel]

I have created some tests: https://github.com/tcort/markdown-link-check/pull/328/files#diff-609278aba9a28dbff1f94a5481c16208f8d0263db1f8784adac9ddac74a18d3a

In the tests I was not able to reproduce this.

I haven't done a proper test. Perhaps the case is so special that it can't be found in the tests.