Bug 799444 - Silent crash on CSV import

Don't try to add a transaction with no splits to the imported
transaction list, gnc_gen_trans_list_add_trans_internal asserts.

gnucash/import-export/csv-imp/assistant-csv-trans-import.cpp

@@ -2188,7 +2188,12 @@ CsvImpTransAssist::assist_match_page_prepare ()
                 draft_trans->m_trec_date ? static_cast<time64>(GncDateTime(*draft_trans->m_trec_date, DayPart::neutral)) : 0,
             };
 
-            gnc_gen_trans_list_add_trans_with_split_data (gnc_csv_importer_gui, std::move (draft_trans->trans), &lsplit);
+//A tramsaction with no splits is invalid and will crash later.
+            if (xaccTransGetSplit(draft_trans->trans, 0))
+                gnc_gen_trans_list_add_trans_with_split_data (gnc_csv_importer_gui, std::move (draft_trans->trans),
+                                                              &lsplit);
+            else
+                xaccTransDestroy(draft_trans->trans);
             draft_trans->trans = nullptr;
         }
     }