OpenUI5 version: 1.60/latest

Browser/version (+device/version): Chrome v73 on Ubuntu (desktop)
Any other tested browsers/devices(OK/FAIL): not tested

URL (minimal example if possible): http://jsfiddle.net/zypA1310/L5cx4fut/

Steps to reproduce the problem:

1. Run the above example (SelectDialog with showClearButton=true and multiSelect=false)
2. Click on the value help button

What is the expected result?
In the opened dialog, there is some way to clear the content inside Input, either the clear button or by clicking confirm with an empty selection.

What happens instead?
In the opened dialog, the clear button is shown but disabled. Confirm button is not shown.

Additional information:
According to the doc, this is the intended way to clear value from Input with valueHelpOnly=true:

We recommended enabling of the Clear button in the following cases, where a mechanism to clear the value is needed: In case of single selection mode(default mode) for Select Dialog and rememberSelections is set to true. Clear button needs to be enabled in order to allow users to clear the selection. In case of using sap.m.Input with valueHepOnly^[sic] set to true, Clear button could be used for clearing selection. In case the application stores a value and uses only Select Dialog to edit/maintain it.

Related: #898.