Detect missing log file segment during initialization

During initialization of multiFilelog, the start and end offsets are interpreted from the log segment file names. If any of the log files are missing, these offsets can be incorrect and must be verified. Additionally, these offsets must also be verified against the offsets in the superblock.

If any of the log.X.data files are deleted, the indexer can run into panic-restart loop. I am able to reproduce this issue locally with the following steps:

• set indexer.plasma.LSSSegmentFileSize to a small size (say 5MB)
• create index and load enough documents to see multiple log.X.data files
• delete some of the log.X.data files and restart indexer