MapScan does not preserve top-level UDT values (returns empty map)

[ribaraka]

When reading rows that contain a top-level UDT column, MapScan(map[string]interface{}) does not preserve the decoded UDT field values, while Scan(&map[string]interface{}) works as expected.

For a top-level frozen<udt> column:

• Scan(...) can decode the UDT correctly
• MapScan(...) returns the row, but the UDT value is an empty map[string]interface{}

Expected behavior

MapScan should preserve top-level UDT contents consistently with Scan
A non-null UDT column should decode into a populated map[string]interface{} containing its field values

This is particularly problematic because:

• The column itself is present
• No error is raised
• The data is silently lost rather than missing or failing loudly

[worryg0d]

Jira ticket - CASSGO-115

[worryg0d]

Patch with fix is already merged to trunk