fix: Make legacy property sturdier

[rafaeelaudibert]

This property might be accessed/called before we've properly initialized feature flags, so let's make sure we're not breaking anything (we have broken it already, see https://posthog.slack.com/archives/C02E3BKC78F/p1734111258352399)

Checklist

• Tests for new code (see advice on the tests we use)
  • No tests for now, but we should add it eventually, we need to guarantee this doesn't break anymore
• Accounted for the impact of any changes across different browsers
• Accounted for backwards compatibility of any changes (no breaking changes in posthog-js!)

[vercel]

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Dec 13, 2024 5:47pm

[github-actions]

Size Change: +660 B (+0.02%)

Total Size: 3.21 MB

Filename	Size	Change
dist/array.full.es5.js	260 kB	+66 B (+0.03%)
dist/array.full.js	363 kB	+66 B (+0.02%)
dist/array.full.no-external.js	362 kB	+66 B (+0.02%)
dist/array.js	178 kB	+66 B (+0.04%)
dist/array.no-external.js	176 kB	+66 B (+0.04%)
dist/main.js	178 kB	+66 B (+0.04%)
dist/module.full.js	363 kB	+66 B (+0.02%)
dist/module.full.no-external.js	362 kB	+66 B (+0.02%)
dist/module.js	178 kB	+66 B (+0.04%)
dist/module.no-external.js	176 kB	+66 B (+0.04%)

ℹ️ View Unchanged

Filename	Size
dist/all-external-dependencies.js	206 kB
dist/customizations.full.js	12.6 kB
dist/dead-clicks-autocapture.js	14.4 kB
dist/exception-autocapture.js	9.48 kB
dist/external-scripts-loader.js	2.48 kB
dist/recorder-v2.js	115 kB
dist/recorder.js	115 kB
dist/surveys-preview.js	57.6 kB
dist/surveys.js	63.3 kB
dist/tracing-headers.js	1.75 kB
dist/web-vitals.js	10.4 kB

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