From coverity: trayItem.getImage may return null

git-svn-id: http://svn.code.sf.net/p/davmail/code/trunk@2259 3d1905a2-6b24-0410-a738-b14d5a86fcbd

src/java/davmail/ui/tray/SwtGatewayTray.java

@@ -78,7 +78,8 @@ public class SwtGatewayTray implements DavGatewayTrayInterface {
         isActive = true;
         display.syncExec(new Runnable() {
             public void run() {
-                if (trayItem.getImage().equals(image)) {
+                Image currentImage = trayItem.getImage();
+                if (currentImage != null && currentImage.equals(image)) {
                     trayItem.setImage(image2);
                 } else {
                     trayItem.setImage(image);