inconsistent naming of sidebar_staff.png in Customer Tool

fixes #48

Author: pinhead84

Customer/src/main/java/de/openindex/support/customer/CustomerFrame.java

@@ -45,6 +45,7 @@
 import javax.swing.event.DocumentEvent;
 import javax.swing.event.DocumentListener;
 import net.miginfocom.swing.MigLayout;
+import org.apache.commons.lang3.ObjectUtils;
 import org.apache.commons.text.StringEscapeUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -117,7 +118,7 @@ public void windowClosing(WindowEvent e) {
 
  // sidebar
  SidebarPanel sidebarPanel = new SidebarPanel(
- ImageUtils.loadImage(CustomerApplication.resource("sidebar_staff.png")),
+ ImageUtils.loadImage(ObjectUtils.defaultIfNull(CustomerApplication.resource("sidebar.png"), CustomerApplication.resource("sidebar_staff.png"))),
  ImageUtils.loadImage(CustomerApplication.resourceBranding())
  );