UJOTYP-30: Fix some problems with function "ujot_variant_type_check"
- change tabulators to spaces
- change several functions returning "UJOT_ERR_INVALID_TYPE", if type is not correct
- rename return parameter of "ujot_variant_type_check" from "result" to "type_is_correct"
- add missing NULL pointer checks in some "ujot_variant_as_xxx" functions
- rename union variable "bool" to "boolean"
- fix logic in test functions
Closes UJOTYP-30