message: Fix break-chains for unhit source blocks
  Summary: Follow-up to {D33332300 (https://github.com/facebook/redex/commit/2f40a75f2cc307cc116a4996a63c95ede3e05232)}.
diff: @@ -589,7 +589,11 @@ class InlineForSpeedDecisionTrees final : public InlineForSpeedBase {
  if (!vals) {
  return -1;
  }
  - return *vals->hits.at(0);
  + const auto& val = vals->hits.at(0);
  + if (!val) {
  + return 0;
  + }
  + return *val;
  };
  auto order = [&](const auto& lhs, const auto& rhs) {
  