Handle more cases of invalid line dash patterns in annotation borders

When an annotation border uses line dash patterns, a valid `Border` entry might be e.g. `[0 0 1 [2 6]]`.
For more about line dash patterns, see https://github.com/mozilla/pdf.js/pull/4080#issue-25177520.

In the PDF file in the issue referenced below, the borders are `[10 10 10 60]`. In the PDF specification it's inferred that the last entry should be an array, but there is no mentioning what should happen if it's not.
When opening the file in Adobe Reader the border is simply ignored, so this patch does the same thing for PDF.js.

Fixes #4766.