Modified hidden input text element lookup to actually find the element. Previously a jQuery selector was used for finding an input[type=hidden] element which is not rendered anymore by ComboBoxRenderer.

Tested with ICEfaces 4 trunk r49532, Tomcat 8, FF 47, Chrome 53, IE 11.
The original console error is resolved however there is a new console error seen when interacting with the comboBox drop arrow after setting the disabled or readOnly attributes to true. Also the comboBox does not appear disabled when that attribute is true.

Uncaught TypeError: Cannot read property 'length' of undefined(…)
combobox.c.js.jsf?ln=icefaces.ace&v=4_2_0_161109:33 

To reproduce:
1.) Use the /comboBoxDynAttribute.jsf application located at:
http://dev.icesoft.com/svn/repo/qa/trunk/Regression-Icefaces4/Sparkle/Nightly/comboBox
2.) Select the rendered checkbox.
3.) Select either the disabled or readOnly checkboxes.
4.) On the rendered comboBox click the down arrow on the right side of the component. At this point the console error appears.

This last issue is not a regression introduced by the previous commit. It is just another issue with the comboBox, orthogonal to the previous issue.

The applied fix modifies the body of clientSideModeUpdate function to execute only when there's a client side configuration defined.

Verified ICEfaces 4 trunk r49534, Tomcat 8, MS edge, IE 11, 10, 9, 8, FF 47, Chrome 53.