Use semantically correct minimum for value range in region growing preview
For certain cases the minimum was set to "min()" instead of "lowest()/NonpositiveMin()" which resulted in semantically wrong minimum values for floating point numbers.
Test Plan: Follow reproduction steps of task.
Reviewers: kalali, O1 MITK Reviewer Group I, floca
Reviewed By: O1 MITK Reviewer Group I, floca
Maniphest Tasks: T28732
Differential Revision: https://phabricator.mitk.org/D556