front-matter parsing causes error and high cpu utilization

[bugrasan]

create a new markdown document with:

---
tags: 
---

# header
text

then save. Afterwards click the "refresh" button on the VSNotes sidebar. Now it will spin endless.

the error is as following:

 abstractExtensionService.ts:400 [patricklee.vsnotes]: Command `vsnotes.listNotes` appears multiple times in the `commands` section.
console.ts:137 [Extension Host] TypeError: parsedFrontMatter.data.tags is not iterable	at /home/user/.vscode/extensions/patricklee.vsnotes-0.7.1/src/treeView.js:166:58
t.log @ console.ts:137