BaseContext :: isValid - Is context valid
The function checks, whether the context handle refers to a valid context instance (true) or not (false). Context handles might become invalid when the resource owning the context has been deleted (e.g. when deleting a property handle, type context and property context are deleted as well).
The function never throws an exception.
Return value: Success ( bool )
The value is true when the function was executed successfully. Otherwise the value is set to false.