Fixed index out of range error in fancy exporter

[apainintheneck]

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.

This is just a small bug that shows up when trying to print entries using the fancy exporter that lack titles. This error doesn't show up with any of the other --format methods as far as I can tell.

Steps to reproduce

1. Use jrnl edit to add a post without a title.
2. Enter jrnl -1.

This change just makes sure that the title_lines list always includes at least one empty string.

[micahellison]

Hi @apainintheneck, I'm having a time running the steps to reproduce. Every time I edit my journal, it keeps a title of some sort, or folds the entry into the previous entry. Could you let me know what specific text you're entering into your editor to get this to work? Thanks.
Never mind! Just figured out - the entry needs to be completely blank except for a space after the timestamp.

Could you add a test for this PR in format.feature?

[apainintheneck]

I was unable to find a way to reproduce this bug with a BDD test. Not sure if it's really necessary either since it's such a small thing.

[wren]

Ok, that makes sense. Thanks!