chore: tweak default value

store/db/sqlite/migration/prod/0.19/00__add_resource_name.sql

@@ -1,10 +1,10 @@
-ALTER TABLE memo ADD COLUMN resource_name TEXT;
+ALTER TABLE memo ADD COLUMN resource_name TEXT NOT NULL DEFAULT "";
 
 UPDATE memo SET resource_name = lower(hex(randomblob(8)));
 
 CREATE UNIQUE INDEX idx_memo_resource_name ON memo (resource_name);
 
-ALTER TABLE resource ADD COLUMN resource_name TEXT;
+ALTER TABLE resource ADD COLUMN resource_name TEXT NOT NULL DEFAULT "";
 
 UPDATE resource SET resource_name = lower(hex(randomblob(8)));