Add <br> as empty representation for webkit (#12490)

Change-Id: Idfb1c770d411b0516046e40852b79da6f9c7916c

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

@@ -403,7 +403,7 @@ public class VRichTextArea extends Composite implements Field, KeyPressHandler,
                 result = "";
             }
         } else if (browser.isWebkit()) {
-            if ("<div><br></div>".equals(result)) {
+            if ("<br>".equals(result) || "<div><br></div>".equals(result)) {
                 result = "";
             }
         } else if (browser.isIE()) {