[FIX] sale_stock: allow to tab past an empty QtyAtDateWidget

Steps to reproduce
==================

- In the settings, check the "Reception Report" option
- Create a new quotation
- Add a line
- Do not select a product
- Press tab a few times

The focus doesn't go past the Quantity widget

Cause of the issue
==================

The next item to be focused when pressing tab is selecting with the
following selector

https://github.com/odoo/odoo/blob/13745d597d03b552fe5f73ca81143a49efb8aa9f/addons/web/static/src/core/utils/ui.js#L159-L161

Since there is a tabindex of 0, the focus will try to go to the
QtyAtDateWidget

Solution
========

Set the tabindex to -1 when no value has been set

opw-3266063

closes odoo/odoo#120005

X-original-commit: 30fcb2e60fed17a473353b21bac4916e9ab77b10
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Hubert Van De Walle <huvw@odoo.com>

addons/sale_stock/static/src/widgets/qty_at_date_widget.xml

@@ -4,7 +4,7 @@
     <!-- TODO: rename this to QtyAtDate in master version -->
     <t t-name="sale_stock.qtyAtDate" owl="1">
         <div t-att-class="!props.record.data.display_qty_widget ? 'invisible' : ''">
-            <a tabindex="0" t-on-click="showPopup" t-attf-class="fa fa-area-chart {{ calcData.forecasted_issue ? 'text-danger' : 'text-primary' }}"/>
+            <a t-att-tabindex="props.record.data.display_qty_widget ? '0' : '-1'" t-on-click="showPopup" t-attf-class="fa fa-area-chart {{ calcData.forecasted_issue ? 'text-danger' : 'text-primary' }}"/>
         </div>
     </t>