Fix a couple of warnings introduced by commit 01420adb99

In addition make the code really use an inner join if no additional conditions are set
which gives better performance on at least postgresql

libgnucash/backend/sql/gnc-transaction-sql.cpp

@@ -260,7 +260,7 @@ load_splits_for_transactions (GncSqlBackend* sql_be, std::string selector)
     if (selector.empty())
     {
 	sql += SPLIT_TABLE ".* FROM " SPLIT_TABLE " INNER JOIN "
-	    TRANSACTION_TABLE " WHERE " SPLIT_TABLE "." + sskey + " = "
+	    TRANSACTION_TABLE " ON " SPLIT_TABLE "." + sskey + " = "
 	    TRANSACTION_TABLE "." + tpkey;
 	selector = "(SELECT DISTINCT " + tpkey + " FROM " TRANSACTION_TABLE ")";
     }
@@ -378,12 +378,20 @@ query_transactions (GncSqlBackend* sql_be, std::string selector)
     if (!instances.empty())
     {
 	const std::string tpkey(tx_col_table[0]->name());
-	if (selector.empty())
-	{
-	    selector = "(SELECT DISTINCT ";
-	    selector += tpkey + " FROM " TRANSACTION_TABLE +")";
-	}
+        if (!selector.empty() && (selector[0] != '('))
+        {
+            auto tselector = std::string ("(SELECT DISTINCT ");
+            tselector += tpkey + " FROM " TRANSACTION_TABLE " WHERE " + selector + ")";
+            selector = tselector;
+        }
+
         load_splits_for_transactions (sql_be, selector);
+
+        if (selector.empty())
+        {
+            selector = "(SELECT DISTINCT ";
+            selector += tpkey + " FROM " TRANSACTION_TABLE ")";
+        }
         gnc_sql_slots_load_for_sql_subquery (sql_be, selector,
 					     (BookLookupFn)xaccTransLookup);
     }