ComboBox: wrong behaviour on BACKSPACE

[ilhan007]

Describe the bug
When you have a "selected" item (the text in the input is matching one of the items)
and start deleting the text with BACKSPACE:

(1) The first BACKSPACE is not deleting anything, just opens the picker
(2) When you delete the last letter of the whole text,
it starts all over, the full text is restored, when you expect to have an empty input field

To reproduce
Steps to reproduce the behavior:

1. Go to http://localhost:8080/test-resources/pages/ComboBox.html
2. Use the first ComboBox with text "Bulgaria"
3. Press BACKSPACE - no letter is deleted
4. Continue pressing BACKSPACE to delete the text
5. When you delete the last letter, it starts all over, the full text of "Bulgaria" is restored

Expected behavior
You should be able to delete the text in the ComboBox with BACKSPACE

Context

• UI5 Web Components version: master
• OS/Platform: {...} MACOS
• Browser (if relevant): {...} Chrome

Affected components (if known)
ui5-combobox