In quick compiler, force string init invoke to be fast path.

Was running into an issue where a secondary dex file was falling back on
the quick compiler, and IsFastInvoke returned 0 because the
referrer_class was nullptr, causing the string init to be slow path. The
string init technically does not have to be fast path, but there's no
reason to duplicate the logic to call off a thread pointer on the slow

Bug: 20870917
Change-Id: I47e1524d939eb7e9b1da8186092fafc6e925009e
1 file changed