ERROR: execute cannot be used while an asynchronous query isunderway

Hi all,

The version of pgAdmin

Version2.0
CopyrightCopyright 2013 - 2017, The pgAdmin Development Team
Python Version2.7.11 (v2.7.11:6d1b6a68f775, Dec 5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)]
Flask Version0.11.1
Application ModeDesktop
Current Userpgadmin4@pgadmin.org

not compiled from source

windows 10

reproduce step:

1. open a query tool for any database in pgadmin 4.
2. create a table like create table abc(name1 varchar(10))
3. write a sql in query tool like insert into abc(name1) values('n');
4. press F5 many times in moment. for example press F5 key 10 times in 2-4 seconds.
5. the query tool would return a message which is ERROR:  execute cannot be used while an asynchronous query is underway