[clang][dataflow] Don't crash when constructing an array of records.

When I wrote https://reviews.llvm.org/D155446, I assumed that a `CXXConstructExpr` would always have record type, but this isn't true: It can have array type when constructing an array of records. The code would crash in this situation because `createValue()` would return null.

This patch includes a test that reproduces the crash without the other changes in the patch.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D156402