Regression in pandocReferenceDefinition

[jez]

#248 caused a regression in pandocReferenceDefinition (reference links):

Consider this snippet:

This is a [link].

[link]: https://example.org

Before #248:

After #248:

[jez]

Specifically, using synstack ⁽¹⁾ to inspect the highlighting groups shows these changes at these positions:

---

[link]: https://example.org
^

Before:

['pandocReferenceDefinition']

After:

['pandocReferenceLabel', 'pandocOperator']

---

[link]: https://example.org
 ^

Before:

['pandocReferenceDefinition', 'pandocReferenceDefinitionLabel']

After:

['pandocReferenceLabel']

---

[link]: https://example.org
        ^

Before:

['pandocReferenceDefinition', 'pandocReferenceDefinitionAddress']

After:

[]

---