[clang] Set the error-bit for ill-formed semantic InitListExpr.

When a semantic checking fails on a syntactic InitListExpr, we will
get an ill-formed semantic InitListExpr (e.g. some inits are nullptr),
using this semantic InitListExpr in clang (without setting the err-bits) is crashy.

Differential Revision: https://reviews.llvm.org/D84140