backtrace.c: skip innermost frame only when the method is in C; #5394

src/backtrace.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) {