Fix: Empty text nodes & text style ids

[sawyerclick]

• Ignore empty text nodes. Previously would error when trying to access textNode.styles, which is false. I could not find a way for the Figma plugin API to ignore empty nodes by default so included safeguards in convertTextFrames.ts.
• Ensure textNode.textStyleId is not a symbol. Text nodes with mixed styles get a symbol as their style id. I added a conditional to ignore that ID and proceed as if none were found. I think that's the right move here but @svickars should double check me.

[changeset-bot[bot]]

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Latest commit: 5a0c853d57ec54ef29f4e3717187ea15f933a007

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ---------- | ----- | | figma2html | Patch |

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