Revert handle subquery pipeline as a different pipeline.

Author: WaVEV

django_mongodb/query.py

@@ -70,8 +70,7 @@ def get_cursor(self):
         return self.collection.aggregate(self.get_pipeline())
 
     def get_pipeline(self):
-        subquery_pipeline = self.subquery.get_pipeline() if self.subquery else []
-        pipeline = []
+        pipeline = self.subquery.get_pipeline() if self.subquery else []
         if self.lookup_pipeline:
             pipeline.extend(self.lookup_pipeline)
         if self.mongo_query:
@@ -90,8 +89,7 @@ def get_pipeline(self):
             pipeline.append({"$skip": self.query.low_mark})
         if self.query.high_mark is not None:
             pipeline.append({"$limit": self.query.high_mark - self.query.low_mark})
-
-        return subquery_pipeline + pipeline
+        return pipeline
 
 
 def join(self, compiler, connection):