Use   in empty table footers to make them render properly (#7718)

svn changeset:23701/svn branch:6.8

src/com/vaadin/terminal/gwt/client/ui/VScrollTable.java

@@ -3425,6 +3425,10 @@ public class VScrollTable extends FlowPanel implements Table, ScrollHandler,
          *            The text in the footer
          */
         public void setText(String footerText) {
+            if (footerText == null || footerText.equals("")) {
+                footerText = " ";
+            }
+
             DOM.setInnerHTML(captionContainer, footerText);
         }