Fix tinyint silent unmarshal error and vector SliceMap bug

Tinyint unmarshal silently errors and unmarshals tinyint values as 0 in some situations.
This patch also removes other cases of silent errors in decode functions.

Fix issue where reading vectors with SliceMap is not possible.

Patch by João Reis; reviewed by James Hartig for CASSGO-82, CASSGO-83

Author: joao-r-reis