Invert text_for_attribute length assertion comparison

[exvacuum]

I was trying to work with markup attributes in my project and would encounter a panic when executing the Line::text_for_attribute function, as it would consistently fail the following assertion:

assert!(
    self.text.len() <= attribute.position + attribute.length,
    "Attribute \"{attribute}\" represents a range not representable by this text: \"{}\". \
Does this MarkupAttribute belong to this MarkupParseResult?",
    self.text
);

This assertion seems to be checking that the text length is shorter than the attribute's range. This pull request just flips the comparison from <= to >=.

[janhohenheim]

Hmm? The original code makes sense to me. If this attribute is pointing past the text, something is wrong.
Edit: whoops, after rethinking, this makes sense. Thanks!