* src/eval.c (get_backtrace): Don't skip the top frame

* src/eval.c (get_backtrace): Don't skip the top frame

`profiler.el` was reporting incomplete backtraces.
I had a suspicion there was something off, but it became obvious
when I saw that `set-buffer-multibyte` did not appear in the
`profiler-report` output when opening a large compressed tarball,
even though I knew it to be a large contributor (which `elp-results`
confirmed).

I have no idea why this `backtrace_next` was there, sadly, but now
`profiler-report` gives me results that make a lot more sense.