Re-added accidentally removed IE 8 workaround for uploads (#9179)

Change-Id: I8b45ee52b402b6fd9ead0905c4a42b284f0e7c99

client/src/com/vaadin/client/ui/VUpload.java

@@ -155,6 +155,8 @@ public class VUpload extends SimplePanel {
     private static native void setEncoding(Element form, String encoding)
     /*-{
       form.enctype = encoding;
+      // For IE8
+      form.encoding = encoding;
     }-*/;
 
     /** For internal use only. May be removed or replaced in the future. */