fix: give chatbot pickups per-leg surcharges including the return leg

tests/Resources/product_export_data.xml

@@ -88,6 +88,8 @@
    <zustiege_rueck>
     <!-- Priced on the return leg only: levelling would copy 3,00 onto the outbound entry. -->
     <zustieg_rueck id="1" idbuspro="27" preis="3,00" />
+    <!-- Listed without a price: BusPro bills the return leg nothing. -->
+    <zustieg_rueck id="2" idbuspro="55" />
    </zustiege_rueck>
   </termin>
   <!-- Unparseable date: its hotel row is dropped and counted. -->