Fix PR8774 by restricting when hasInit returns true. Previously, it

Fix PR8774 by restricting when hasInit returns true. Previously, it
would return true if the initializer pointer union had *any* non-null
pointer in it, even if the pointer wasn't one that would actually be
returned via getInit(). This makes it more accurately model the logic of
'getInit() != NULL'.

This still isn't completely satisfying. From a principled stance,
I suspect we should make hasInit() and getInit() *always* return false
and NULL (resp.) for ParmVarDecl. We shouldn't at the API level treat
initializers and default arguments as the same thing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@121692 91177308-0d34-0410-b5e6-96231b3b80d8