Adds missing case to assigns clause type checking

[feliperodri]

Signed-off-by: Felipe R. Monteiro felisous@amazon.com

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[kroening]

BTW, convert_type is likely the wrong place to do the check. I'd move it to the typechecker.

[martin-cs]

The changes to convert_type look good but I think the array changes should be handled separately.

[feliperodri]

#6234 includes this fix.