message: Fix `show()` for coalesced source blocks
  Summary: Overlooked.
diff: @@ -1467,10 +1467,12 @@ std::ostream& operator<<(std::ostream& o, const MethodItemEntry& mie) {
  o << "POSITION: " << *mie.pos;
  break;
  case MFLOW_SOURCE_BLOCK:
  - o << "SOURCE-BLOCK: " << show(mie.src_block->src) << "@"
  - << mie.src_block->id;
  + o << "SOURCE-BLOCKS:";
  +
  + for (auto* sb = mie.src_block.get(); sb != nullptr; sb = sb->next.get()) {
  + o << " " << show(sb->src) << "@" << sb->id;
  o << "(";
  - for (const auto& val : mie.src_block->vals) {
  + for (const auto& val : sb->vals) {
  if (val) {
  o << val->val << ":" << val->appear100;
  } else {
  @@ -1479,6 +1481,7 @@ std::ostream& operator<<(std::ostream& o, const MethodItemEntry& mie) {
  o << "|";
  }
  o << ")";
  + }
  break;
  case MFLOW_FALLTHROUGH:
  o << "FALLTHROUGH";
  