[Sema] Don't assume that an initializer list has an initializer

[Sema] Don't assume that an initializer list has an initializer

Given something like 'int({}, 1)', we would try to emit a diagnostic
regarding the excess element in the scalar initializer.  However, we
assumed that the initializer list had an element in it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234565 91177308-0d34-0410-b5e6-96231b3b80d8