Fix 1203471: Incorrect rationalization of unused SIMD localVar

Fix 1203471: Incorrect rationalization of unused SIMD localVar

The Rationalizer was not correctly handling a case of an unused SIMD expression involving a localVar or temporary value, where the SIMD expression is returning a non-SIMD value, and the expression is sufficiently complex (e.g. a call to vector * scalar which is inlined but not an intrinsic).
The ldobj of the localVar is not eliminated, because it involves an indirection, and therefore appears potentially unsafe to eliminate. However, when we transform the ldobj into a plain localVar during the Rationalizer, we need to correctly handle the case where it has no parent.

[tfs-changeset: 1505976]