Fix bug when trying to remove station & none selected

src/main/java/name/nathanmcrae/numbersstation/StationSelectionController.java

@@ -112,6 +112,9 @@ public class StationSelectionController {
     @FXML
     private void handleRemoveButtonPress(ActionEvent event) {
         int selectedIndex = stationListView.getSelectionModel().getSelectedIndex();
+        if (selectedIndex < 0) {
+            return;
+        }
         StationSettings station = stationList.get(selectedIndex);
         String stationName = station.toString();