Correct logic error found by inspection.

From Jim's post on the lldb-dev mailing list:

  This code is there as a backstop for when the unwinder drops a frame at
  the beginning of new function/trampoline or whatever.

  In the (older_ctx_is_equivalent == false) case we will see if we are at
  a trampoline function that somebody knows how to get out of, and
  otherwise we will stop.