Don't crash on surprising tokens in default parameter template lists.

Fixes this snippet from SLi's afl fuzzer output:

  class {
      i (x = <, enum

This parsed i as a function, x as a paramter, and the stuff after < as a
template list.  This then called TryConsumeDeclarationSpecifier() which
called TryAnnotateCXXScopeToken() without checking the preconditions of
this function.  Check them before calling, like all other callers of
TryAnnotateCXXScopeToken() do.

A more readable reproducer that causes the same crash is

  class {
      void i(int x = MyTemplateClass<int, union int>::foo());
  };

The reduced version used an eof token as surprising token, but kw_int works
just as well to repro and is easier to insert into a test file.

llvm-svn: 224906