DateSortedList Sorting bug fix

app/src/main/java/de/sebse/fuplanner/tools/DateSortedList.java

@@ -7,6 +7,7 @@ import java.util.Iterator;
 
 public abstract class DateSortedList<T> extends ArrayList<T> {
     private int split = -1;
+    private boolean mSorting = false;
 
     public T getPast(int index) {
         if (split < 0)
@@ -30,6 +31,7 @@ public abstract class DateSortedList<T> extends ArrayList<T> {
 
     @Override
     public T get(int index) {
+        if (mSorting) return super.get(index);
         if (split < 0)
             sort();
         if (reversed())
@@ -55,6 +57,7 @@ public abstract class DateSortedList<T> extends ArrayList<T> {
     }
 
     public void sort() {
+        mSorting = true;
         Collections.sort(this, ((e1, e2) -> Long.compare(getDateByItem(e1), getDateByItem(e2))));
         long now = System.currentTimeMillis();
         split = 0;
@@ -64,6 +67,7 @@ public abstract class DateSortedList<T> extends ArrayList<T> {
             else
                 break;
         }
+        mSorting = false;
     }
 
     public Iterator<T> getEventsOfMonth(int year, int month) {