Guard against fetch failures in textPositions

[allanlasser]

Fixes #939

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Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	30.99%	6807 / 21964
🔵	Statements	30.99%	6807 / 21964
🔵	Functions	49.11%	276 / 562
🔵	Branches	75.52%	1037 / 1373

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/lib/api/documents.ts	91.5%	89.47%	96.96%	91.5%	89-108, 179-181, 186-187, 204-210, 516-518
src/lib/api/tests/documents.test.ts	98.81%	98.96%	88.88%	98.81%	653-660

Generated in workflow #446 for commit 9fae072 by the Vitest Coverage Report Action

[eyeseast]

I don't think we're actually calling this function anywhere, since we use embedded text in PDFs, but this seems like a good change in case we do start using it.