🐛 fix research-and-writing links still rendering on bake even when content is invalid

[ikesau]

The research and writing block had an incorrectly implemented fallback for when linked documents were invalid.

If there's an error and we're previewing, we show a red warning block. If we're not previewing (i.e. baking), we should return null.

This was noticed because an unpublished gdoc that was being linked to in the CO₂ topic page was showing up as an empty tile.

[owidbot]

Quick links (staging server):

Site	Admin	Wizard

Login: ssh owid@staging-site-research-and-writing-component-error-rendering

• Site-screenshots: https://github.com/owid/site-screenshots/compare/research-and-writing-component-error-rendering
• SVG tester: https://github.com/owid/owid-grapher-svgs/compare/research-and-writing-component-error-rendering

SVG tester:

Number of differences (default views): 0
Number of differences (all views): 0

Edited: 2024-05-15 18:47:09 UTC
Execution time: 1.17 seconds

[mlbrgl]

Makes sense, thanks!

Confirmed locally (dev and bake)