[import-backend.cpp] gnc_import_exists_online_id shouldn't destroy transaction

Because gnc_import_exists_online_id is documented to only check that
the online_id already exists. It is more appropriate for its caller to
destroy the transaction.

gnucash/import-export/import-backend.cpp

@@ -1033,15 +1033,6 @@ gboolean gnc_import_exists_online_id (Transaction *trans, GHashTable* acct_id_ha
     }
 
     auto online_id_exists = g_hash_table_contains (online_id_hash, source_online_id);
-    
-    /* If it does, abort the process for this transaction, since it is
-       already in the system. */
-    if (online_id_exists)
-    {
-        DEBUG("%s", "Transaction with same online ID exists, destroying current transaction");
-        xaccTransDestroy(trans);
-        xaccTransCommitEdit(trans);
-    }
     g_free (source_online_id);
     return online_id_exists;
 }

gnucash/import-export/import-main-matcher.cpp

@@ -2225,7 +2225,14 @@ gnc_gen_trans_list_add_trans_internal (GNCImportMainMatcher *gui, Transaction *t
     g_assert (trans);
 
     if (gnc_import_exists_online_id (trans, gui->acct_id_hash))
+    {
+        /* If it does, abort the process for this transaction, since
+           it is already in the system. */
+        DEBUG("%s", "Transaction with same online ID exists, destroying current transaction");
+        xaccTransDestroy(trans);
+        xaccTransCommitEdit(trans);
         return;
+    }
 
     Split *split = xaccTransGetSplit (trans, 0);
     Account *acc = xaccSplitGetAccount (split);