1975 - qed crash@in bool std::operator< <char, std::char_traits<char>

1975 - qed crash@in bool std::operator< <char, std::char_traits<char>
If cassandra returns empty columns for a key or if a select field is not present in the columns returned by cassandra, then an empty string is added for the column value.
In PostProcessingQuery::sort_field_comparator(), lhs_val and rhs_val are not initialized, resulting in junk value when the column value is empty string => stringToInteger() doesn’t update the lhs_val and rhs_val for invalid input. This causes std::sort() to access invalid memory resulting in segfault.

1659 - qed cored at SelectQuery::process_object_query_specific_select_params
If cassandra returns empty row for a key in object query, then the search for SANDESH_TYPE column in SelectQuery::process_object_query_specific_select_params() fails resulting in assert.
Added code to skip the row, if the column values returned by cassandra is empty.