Fix Bugzilla 20872 - std.array.assocArray trusts user-provided 'front…

[ntrel]

…' for values

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20872	normal	std.array.assocArray trusts user-provided 'front' for values

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 "master + phobos#9036"