Add partial index on SQLite

utilities/migrations/sqlite.sql

@@ -21,3 +21,7 @@ DROP TABLE lutim;
 -- 2 up
 ALTER TABLE lutim ADD COLUMN iv TEXT;
 -- 2 down
+-- 3 up
+CREATE INDEX IF NOT EXISTS empty_short_idx ON lutim (short) WHERE path IS NULL;
+-- 3 down
+DROP INDEX empty_short_idx;