Initialize `Allocation` to eliminate compile error

Class `Allocation` is not initialized and I will get a compile error like this.
```
error: ‘worklist.absl::lts_20220623::InlinedVector<absl::lts_20220623::cord_internal::CordRep*, 2, std::allocator<absl::lts_20220623::cord_internal::CordRep*> >::storage_.absl::lts_20220623::inlined_vector_internal::Storage<absl::lts_20220623::cord_internal::CordRep*, 2, std::allocator<absl::lts_20220623::cord_internal::CordRep*> >::data_.absl::lts_20220623::inlined_vector_internal::Storage<absl::lts_20220623::cord_internal::CordRep*, 2, std::allocator<absl::lts_20220623::cord_internal::CordRep*> >::Data::allocated.absl::lts_20220623::inlined_vector_internal::Storage<absl::lts_20220623::cord_internal::CordRep*, 2, std::allocator<absl::lts_20220623::cord_internal::CordRep*> >::Allocated::allocated_capacity’ may be used uninitialized [-Werror=maybe-uninitialized]
```

absl/container/internal/inlined_vector.h

@@ -120,8 +120,8 @@ struct DestroyAdapter<A, /* IsTriviallyDestructible */ true> {
 
 template <typename A>
 struct Allocation {
-  Pointer<A> data;
-  SizeType<A> capacity;
+  Pointer<A> data = nullptr;
+  SizeType<A> capacity = 0;
 };
 
 template <typename A,