bugfix in course modification option

src/main/java/de/thdeg/grademanager/gui/CourseModificationController.java

@@ -123,14 +123,17 @@ public class CourseModificationController {
 
                 course.setName(name.getText());
                 if(semesterComboBox.getValue() != null){
+                    semester = semesterComboBox.getValue();
                     course.setSemester(semester.getSemester());
                 }
                 if(courseTypeComboBox.getValue() != null){
+                    courseType = courseTypeComboBox.getValue();
                     course.setCourseType(courseType.getCourseType());
                 }
                 course.setSws(Integer.parseInt(sws.getText()));
                 course.setEcts(Double.parseDouble(ects.getText()));
                 if(examTypeComboBox.getValue() != null){
+                    examType = examTypeComboBox.getValue();
                     course.setExamType(examType.getExamType());
                 }