db.sqlite: fix exec_param_many bug (#21008)

vlib/db/sqlite/sqlite.c.v

@@ -315,6 +315,9 @@ pub fn (db &DB) exec_param_many(query string, params []string) ![]Row {
 	for {
 		res = C.sqlite3_step(stmt)
 		if res != sqlite.sqlite_row {
+			if rows.len == 0 && is_error(res) {
+				return db.error_message(res, query)
+			}
 			break
 		}
 		mut row := Row{}

vlib/db/sqlite/sqlite_test.v

@@ -95,3 +95,22 @@ fn test_alias_db() {
 	create_host(sqlite.connect(':memory:')!)!
 	assert true
 }
+
+fn test_exec_param_many() {
+	$if !linux {
+		return
+	}
+	mut db := sqlite.connect(':memory:') or { panic(err) }
+	assert db.is_open
+	db.exec('drop table if exists users')!
+	db.exec("create table users (id integer primary key, name text default '' unique);")!
+	db.exec("insert into users (name) values ('Sam')")!
+	db.exec_param_many('insert into users (id, name) values (?, ?)', [
+		'60',
+		'Sam',
+	]) or {
+		assert err.code() == 19 // constraint failure
+		return
+	}
+	assert false
+}