fix issue 20264 - ICE on illegal cast to vector.

[ghost]

An assert failed in AssignExpr sema because the VectorExp created for a particular case of cast was not analysed and hence had not type.
With the fix, and since the cast was illegal, a valid TypeError is now present.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20264	critical	ICE on illegal cast to vector.

Testing this PR locally

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

dub fetch digger
dub run digger -- build "stable + dmd#10532"