orm: fix select .. limit 1 . This case now returns an ?Row.

vlib/pg/pg.v

@@ -29,6 +29,7 @@ pub:
   host string
   user string
   password string
+  dbname string
 }
 
 fn C.PQconnectdb(a byteptr) *C.PGconn
@@ -106,22 +107,23 @@ pub fn (db DB) exec(query string) []pg.Row {
 	return res_to_rows(res)
 }
 
-pub fn (db DB) exec_one(query string) pg.Row {
+fn rows_first_or_empty(rows []pg.Row) pg.Row? {
+	if rows.len == 0 {
+		return error('no row')
+	} 
+	return rows[0]
+}
+            
+pub fn (db DB) exec_one(query string) pg.Row? {
 	res := C.PQexec(db.conn, query.str)
 	e := string(C.PQerrorMessage(db.conn))
 	if e != '' {
-		println('pg exec error:')
-		println(e)
-		return Row{} 
+		return error('pg exec error: "$e"')
 	}
-	rows := res_to_rows(res)
-	if rows.len == 0 {
-		return Row{} 
-	} 
-	return rows[0] 
+	row := rows_first_or_empty( res_to_rows(res) )
+	return row
 }
 
-
 // 
 pub fn (db DB) exec_param2(query string, param, param2 string) []pg.Row {
 	mut param_vals := [2]byteptr