Use internal shipment location to compute warehouse of transit stock move

When the location is the transit location, the warehouse to be used is the
warehouse of the corresponding location on the internal shipment.

Closes #12746

modules/stock/move.py

@@ -683,11 +683,27 @@ class Move(Workflow, ModelSQL, ModelView):
 
     @property
     def from_warehouse(self):
-        return self.from_location.warehouse
+        pool = Pool()
+        ShipmentInternal = pool.get('stock.shipment.internal')
+        warehouse = self.from_location.warehouse
+        if (not warehouse
+                and isinstance(self.shipment, ShipmentInternal)
+                and self.from_location == getattr(
+                    self.shipment, 'transit_location', None)):
+            warehouse = self.shipment.from_location.warehouse
+        return warehouse
 
     @property
     def to_warehouse(self):
-        return self.to_location.warehouse
+        pool = Pool()
+        ShipmentInternal = pool.get('stock.shipment.internal')
+        warehouse = self.to_location.warehouse
+        if (not warehouse
+                and isinstance(self.shipment, ShipmentInternal)
+                and self.to_location == getattr(
+                    self.shipment, 'transit_location', None)):
+            warehouse = self.shipment.to_location.warehouse
+        return warehouse
 
     @property
     def warehouse(self):