Fix wraparound in SstFileManager

Summary: The OnAddFile cur_compactions_reserved_size_ accounting causes wraparound when re-opening a database with an unowned SstFileManager and during recovery. It was introduced in facebook#4164 which addresses out of space recovery with an unclear purpose. Compaction jobs do this accounting via EnoughRoomForCompaction/OnCompactionCompletion and to my understanding would never reuse a sst file name.

Differential Revision: D62535775

file/sst_file_manager_impl.cc

@@ -99,6 +99,7 @@ void SstFileManagerImpl::OnCompactionCompletion(Compaction* c) {
       size_added_by_compaction += filemeta->fd.GetFileSize();
     }
   }
+  assert(cur_compactions_reserved_size_ >= size_added_by_compaction);
   cur_compactions_reserved_size_ -= size_added_by_compaction;
 }
 
@@ -450,7 +451,6 @@ void SstFileManagerImpl::OnAddFileImpl(const std::string& file_path,
     // File was added before, we will just update the size
     total_files_size_ -= tracked_file->second;
     total_files_size_ += file_size;
-    cur_compactions_reserved_size_ -= file_size;
   } else {
     total_files_size_ += file_size;
   }