Fix last time step access for data with arbitrary time geometry

Summary:
In order to access the last time step the

In order to correctly access the last time steps, the time steps have to be increased with each iteration. This will allow to include time points that are exactly equal to the upper bound of the maximum time points.

Test Plan: - unit test with CppUnit

Reviewers: MITK Reviewer Group I, O1 MITK Core, floca

Reviewed By: MITK Reviewer Group I, O1 MITK Core, floca

Maniphest Tasks: T24766

Differential Revision: https://phabricator.mitk.org/D214