Don't consider records with a NULL identifier as a name for typo correction.

Because in C++, "anonymous" doesn't mean "nameless" for records. In
other words, RecordDecl::isAnonymousStructOrUnion only returns true if
the record lacks a name *and* is not used as the type in an object's
declaration.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200868 91177308-0d34-0410-b5e6-96231b3b80d8