fix in statistics filter button

src/de/tudarmstadt/informatik/hostage/ui2/fragment/StatisticsFragment.java

@@ -635,7 +635,7 @@ public class StatisticsFragment extends Fragment implements ChecklistDialog.Chec
 
     /**Paints the filter button if the current filter object is set.*/
     private void actualiseFilterButton(){
-        if (this.filter.isSet() ){
+        if ((this.filter.isSet() && (!(this.currentPlotView instanceof BarGraph))|| (this.filter.hasATimestamp() || this.filter.hasBSSIDs() || this.filter.hasESSIDs()))){
             ImageButton filterButton = this.getFilterButton();
             if (filterButton != null){
                 filterButton.setImageResource(R.drawable.ic_filter_pressed);