message: parser: Create common reference to current control frame
diff: @@ -71,6 +71,8 @@ parser_result<Code> parse_expr(const uint8_t* pos, const uint8_t* end, bool have
  if (pos == end)
  throw parser_error{"Unexpected EOF"};
  + const auto& frame = control_stack.top();
  +
  const auto instr = static_cast<Instr>(*pos++);
  switch (instr)
  {
  @@ -230,7 +232,6 @@ parser_result<Code> parse_expr(const uint8_t* pos, const uint8_t* end, bool have
  {
  if (control_stack.size() > 1)
  {
  - const auto& frame = control_stack.top();
  if (frame.instruction != Instr::loop) // If end of block/if/else instruction.
  {
  const auto target_pc = static_cast<uint32_t>(code.instructions.size() + 1);
  @@ -291,7 +292,6 @@ parser_result<Code> parse_expr(const uint8_t* pos, const uint8_t* end, bool have
  case Instr::else_:
  {
  - const auto& frame = control_stack.top();
  if (frame.instruction != Instr::if_)
  throw parser_error{"unexpected else instruction (if instruction missing)"};
  const auto target_pc = static_cast<uint32_t>(code.instructions.size() + 1);
  