Regression: bayesian matching in csv import doesn't find account

This regression was introduced while improving import of
multi currency transactions.

gnucash/import-export/import-backend.cpp

@@ -301,7 +301,11 @@ gnc_import_TransInfo_set_last_split_info (GNCImportTransInfo *info,
             info->lsplit_amount = lsplit->amount;
             info->lsplit_amount_selected_manually = true;
         }
-        info->dest_acc = lsplit->account;
+        /* Bayesian matching may have already set a candidate destination
+         * account. However if the csv data also provides one, the one from the
+         * csv data is preferred. */
+        if (lsplit->account)
+            info->dest_acc = lsplit->account;
         info->lsplit_rec_state = lsplit->rec_state;
         info->lsplit_rec_date = lsplit->rec_date;
     }