Fix desktopSize parameter issue

desktopSize preference was being applied even if the checkbox was
unselected in the dialog is a value had previously been stored in
the preferences file.
diff --git a/java/com/tigervnc/vncviewer/CConn.java b/java/com/tigervnc/vncviewer/CConn.java
index 5ce1c2f..71bd090 100644
--- a/java/com/tigervnc/vncviewer/CConn.java
+++ b/java/com/tigervnc/vncviewer/CConn.java
@@ -1208,11 +1208,9 @@
         Security.DisableSecType(Security.secTypeX509Ident);
       }
     }
-    if (options.desktopSize.isSelected()) {
-      String desktopSize =
-        options.desktopWidth.getText() + "x" + options.desktopHeight.getText();
-      viewer.desktopSize.setParam(desktopSize);
-    }
+    String desktopSize = (options.desktopSize.isSelected()) ?
+        options.desktopWidth.getText() + "x" + options.desktopHeight.getText() : "";
+    viewer.desktopSize.setParam(desktopSize);
     if (options.fullScreen.isSelected() ^ fullScreen)
       toggleFullScreen();
   }