dynamodb2 was evaluating ProjectionExpression on the wrong local result set

moto/dynamodb2/models.py

@@ -493,7 +493,8 @@ class Table(BaseModel):
 
         if projection_expression:
             expressions = [x.strip() for x in projection_expression.split(',')]
-            for result in copy.deepcopy(possible_results):
+            results = copy.deepcopy(results)
+            for result in results:
                 for attr in list(result.attrs):
                     if attr not in expressions:
                         result.attrs.pop(attr)