Don't allow deletion of some receiving data rows on mobile

specifically, rows on a truck dump parent, which originated from a child
batch (and therefore presumably, an invoice)

tailbone/views/purchasing/receiving.py

@@ -279,9 +279,29 @@ class ReceivingBatchView(PurchasingBatchView):
     def row_deletable(self, row):
         batch = row.batch
 
-        # can always delete rows from truck dump parent
+        # don't allow if master view has disabled that entirely
+        if not self.rows_deletable:
+            return False
+
+        # can never delete rows for complete/executed batches
+        # TODO: not so sure about the 'complete' part though..?
+        if batch.executed or batch.complete:
+            return False
+
+        # can "always" delete rows from truck dump parent...
         if batch.is_truck_dump_parent():
-            return True
+
+            # ...but only on desktop!
+            if not self.mobile:
+                return True
+
+            # ...for mobile we only allow deletion of rows which did *not* come
+            # from a child batch, i.e. can delete ad-hoc rows only
+            # TODO: should have a better way to detect this; for now we rely on
+            # the fact that only rows from an invoice or similar would have
+            # order quantities
+            if not (row.cases_ordered or row.units_ordered):
+                return True
 
         # can always delete rows from truck dump child
         elif batch.is_truck_dump_child():