Fix Issue 20750 - checkaction=context segfaults for null references

[MoonlightSentinel]

No description provided.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20750	minor	checkaction=context segfaults for null references

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + druntime#3045"

[Geod24]

I can see this creating some bloat, though. But at the same time, trying to reduce the bloat will lead to issues with attributes.

[MoonlightSentinel]

Should this be inlined instead of an additional function?

EDIT: Amended to move the check inside of miniFormat

[MoonlightSentinel]

Sqashed the inline changes into the first commit.