Be more eager about setting the 'Invalid' bit on an invalid class

Be more eager about setting the 'Invalid' bit on an invalid class
template instantiation. I wasn't able to reproduce this down to
anything small enough to put in our test suite, but it's "obviously"
okay to set the invalid bit earlier and precludes a
known-broken-but-not-marked-broken class from being used elsewhere.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159584 91177308-0d34-0410-b5e6-96231b3b80d8