fix: app_count of dataset is error when apps was deleted (#4810)

api/models/dataset.py

@@ -76,7 +76,8 @@ class Dataset(db.Model):
 
     @property
     def app_count(self):
-        return db.session.query(func.count(AppDatasetJoin.id)).filter(AppDatasetJoin.dataset_id == self.id).scalar()
+        return db.session.query(func.count(AppDatasetJoin.id)).filter(AppDatasetJoin.dataset_id == self.id,
+                                                                      App.id == AppDatasetJoin.app_id).scalar()
 
     @property
     def document_count(self):