[AdamMagued]

When BytesQueue allocates additional memory, it may insert a dummy/padding entry into the queue to fill fragmented space between tail and head. Such dummy entries can have a length shorter than the minimum header size (headersSizeInBytes = 18, e.g. 0 to 17 bytes).

During expiration or eviction in cleanUp, Set, or onEvict, isExpired and removeOldestEntry attempt to decode headers from the entry. Without checking len(oldestEntry) < headersSizeInBytes, slicing or binary decoding triggered a runtime slice bounds out of range panic (runtime error: index out of range [7] with length 0).

Changes:

• In shard.go:
  • In isExpired, safely check len(oldestEntry) < headersSizeInBytes and return true so dummy/padding entries are evicted safely.
  • In removeOldestEntry, verify len(oldest) >= headersSizeInBytes before decoding the hash or invoking onRemove.
  • In entry retrieval and delete methods, guard against entries shorter than headersSizeInBytes.
• In encoding.go:
  • Add slice bounds checks to readEntry, readTimestampFromEntry, readKeyFromEntry, compareKeyFromEntry, readHashFromEntry, and resetHashFromEntry.
• Add unit tests in shard_test.go, bigcache_test.go, and encoding_test.go verifying that short entries (< 18 bytes) do not cause panics during eviction or decoding.

Fixes #312