Fix redaction box drawing logic

[allanlasser]

Fixes #969

As a bonus, slight improvement to annotation box drawing logic, too!

Doesn't consolidate the logic, since it depends on global variables to work correctly. Could be revisited in the future.

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[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	31.7%	7638 / 24093
🔵	Statements	31.7%	7638 / 24093
🔵	Functions	47.74%	338 / 708
🔵	Branches	75.73%	1108 / 1463

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/lib/components/viewer/AnnotationLayer.svelte	0%	0%	0%	0%	1-280
src/lib/components/viewer/RedactionLayer.svelte	0%	0%	0%	0%	1-135

Generated in workflow #505 for commit f416051 by the Vitest Coverage Report Action