Fix missing rows when reading 2.1 SSTables with static columns in 3.0

If a partition has a static row and is large enough to be indexed, then firstName of the first index block will be set to a static clustering. When deserializing the column index we then incorrectly deserialize the firstName as a regular, non-STATIC Clustering - a singleton array with an empty ByteBuffer to be exact. Depending on the clustering comparator, this can trip up binary search over IndexInfo list and cause an incorrect resultset to be returned.