codegen_scope should not keep old iseq ptr from irep

mrbgems/mruby-compiler/core/codegen.c

@@ -2713,7 +2713,7 @@ scope_new(mrb_state *mrb, codegen_scope *prev, node *lv)

  p->icapa = 1024;
  p->iseq = (mrb_code*)mrb_malloc(mrb, sizeof(mrb_code)*p->icapa);
  p->irep->iseq = p->iseq;
  p->irep->iseq = NULL;

  p->pcapa = 32;
  p->irep->pool = (mrb_value*)mrb_malloc(mrb, sizeof(mrb_value)*p->pcapa);