editor submits <br/> on empty input

[n0weak]

When no text is entered into the editor, "<br/>" is submitted instead of empty string. This leads to inability to apply not-blank constraints without manually checking whether input is "<br/>.

Steps to reproduce the problem:
1. Open labs showcase: http://www.primefaces.org/showcase-labs/ui/editor.jsf
2. Open "Network" tab in development tool for your browser
3. Enter any text into editor, delete all text entered and click submit button.
4. Verify that form:editor_input parameter with value <br/> was sent to the server.