[FIX] point_of_sale: order selector buttons

On to many open orders the + and - buttons will be pushed out of view.
This makes it impossible to close orders without checking out.

addons/point_of_sale/static/src/css/pos.css

@@ -436,6 +436,8 @@ td {
     display: flex;
     -webkit-flex: 1;
     flex: 1;
+    max-width: -moz-available;
+    max-width: -webkit-fill-available;
 }
 .pos .orders {
     display: -webkit-flex;