MB-62124: Dealing with bolt panics while reading (#2043)

- Added checks for cases where bolt buckets are nil

Author: Likith101

index/scorch/persister.go

@@ -829,6 +829,10 @@ func (s *Scorch) loadSnapshot(snapshot *bolt.Bucket) (*IndexSnapshot, error) {
 	for k, _ := c.First(); k != nil; k, _ = c.Next() {
 		if k[0] == boltInternalKey[0] {
 			internalBucket := snapshot.Bucket(k)
+			if internalBucket == nil {
+				_ = rv.DecRef()
+				return nil, fmt.Errorf("internal bucket missing")
+			}
 			err := internalBucket.ForEach(func(key []byte, val []byte) error {
 				copiedVal := append([]byte(nil), val...)
 				rv.internal[string(key)] = copiedVal
@@ -1201,6 +1205,9 @@ func (s *Scorch) rootBoltSnapshotMetaData() ([]*snapshotMetaData, error) {
 			}
 
 			snapshot := snapshots.Bucket(sk)
+			if snapshot == nil {
+				continue
+			}
 			metaBucket := snapshot.Bucket(boltMetaDataKey)
 			if metaBucket == nil {
 				continue

index/scorch/rollback.go

@@ -89,6 +89,10 @@ func RollbackPoints(path string) ([]*RollbackPoint, error) {
 		for j, _ := c2.First(); j != nil; j, _ = c2.Next() {
 			if j[0] == boltInternalKey[0] {
 				internalBucket := snapshot.Bucket(j)
+				if internalBucket == nil {
+					err = fmt.Errorf("internal bucket missing")
+					break
+				}
 				err = internalBucket.ForEach(func(key []byte, val []byte) error {
 					copiedVal := append([]byte(nil), val...)
 					meta[string(key)] = copiedVal