bug#13336: 24.3.50; `next-frame' should not choose a frame (e.g. *Backtrace*) that did not exist when it was invoked

[npostavs]

retitle 13336 `next-frame' should not choose the *Backtrace* frame while 
debugging
quit

Drew Adams <drew.adams@oracle.com> writes:
>
> At least in the case of *Backtrace*, which is perhaps a special
> case, it makes no difference whether the frame exists by the
> time `next-frame' is called.  Backtrace acts specially: it does
> not take its own context into account, but instead reflects the
> state of the rest of Emacs.  The debugger should not return the
> *Backtrace* frame.

Ah okay, a special case for *Backtrace* could make sense.  Although I
forsee some tricky edge cases since *Backtrace* is a buffer, not a
frame.