r175982 - PR15338: Don't assert if -fsanitize=bounds sees array indexing on an incomplete

[Sean Silva]

-      else if (const VariableArrayType *VAT = cast<VariableArrayType>(AT))

Isn't this tautological? I thought that cast<> required its argument
to be nonnull (and hence this would always be true (or otherwise UB)).
If not, then the existence of cast_or_null<> seems suspect.

-- Sean Silva