inputCalendar with converter loses value data during rendering when renderAsPopup=true

t:inputCalendar's implicit and transient inputText gets assigned the
same converter as inputCalendar when isRenderAsPopup=true.

This doesn't work well since the inputCalendar converter is expected
to work on Date objects, and the inputText has a string representation
of the date.

The conversion fails in RendererUtils.getStringValue(facesContext,
component) at converter.getAsString(facesContext, component, value),
and the value in the inputCalender gets lost on rendering.

The value assigned to the inputText is already converted using the inputCalendar's converter during encode, and the component doesn't exist during decode, so the converter needs to be nullified for inputText.