Fix cursor prefetch regression

Author: elprans

asyncpg/connection.py

@@ -120,7 +120,7 @@ async def _get_statement(self, query, timeout):
 
         return state
 
-    def cursor(self, query, *args, prefetch=50, timeout=None):
+    def cursor(self, query, *args, prefetch=None, timeout=None):
         return cursor.CursorInterface(self, query, None, args,
                                       prefetch, timeout)
 

asyncpg/prepared_stmt.py

@@ -41,7 +41,7 @@ def get_attributes(self):
         self.__check_open()
         return self._state._get_attributes()
 
-    def cursor(self, *args, prefetch=50,
+    def cursor(self, *args, prefetch=None,
                timeout=None) -> cursor.CursorInterface:
         """Return a *cursor interface* for the prepared statement.