backtrace.c: skip innermost frame only when the method is in C;
@@ -62,7 +62,7 @@ each_backtrace(mrb_state *mrb, ptrdiff_t ciidx, each_backtrace_func func, void *
idx = (uint32_t)(pc - irep->iseq);
loc.lineno = mrb_debug_get_line(mrb, irep, idx);
- if (n++ == 0 && loc.lineno == -1) continue;
+ if (n++ == 0 && loc.lineno == -1 && ci->acc < 0) continue;
loc.filename = mrb_debug_get_filename(mrb, irep, idx);
if (!loc.filename) {
