Fix parsing Prepared response in V4 protocol.

According to the spec, the format of Prepared metadata is:

<flags><columns_count><pk_count>[<pk_index_1>...<pk_index_n>][<global_table_spec>?<col_spec_1>...<col_spec_n>]

• pk_index_i is a short.
• pk_index_i come before col_spec_i.
• The NO_METADATA flag is not applicable.