[BUG] Multiple email queues for same messages, on exporting via Email.

Description:

On exporting the messages via email, When a user clicks multiple times on Send, the email for sending the export messages
is queued multiple times.

Steps to reproduce:

1. Open any Channel, Go to 3 dots on the Top-Right Corner.
2. Click on Export messages.
3. Select Send via email, and fill in all the details and select the messages.
4. Try clicking multiple times on Send

Expected behavior:

Expected behaviour should be, Once the email is successfully queued for the export, the Contextual Bar must be closed.

Actual behavior:

We can queue as my Export emails.

Server Setup Information:

• Version of Rocket.Chat Server: 3.14.0-develop
• Operating System: Gitpod-linux
• Deployment Method:
• Number of Running Instances:
• DB Replicaset Oplog:
• NodeJS Version: 12.22.1 - x64
• MongoDB Version: 4.2.8

Client Setup Information

• Desktop App or Browser Version:
• Operating System:

Additional context

https://user-images.githubusercontent.com/53378650/115973268-486e2e80-a571-11eb-8473-82c4654a8d33.mp4

Relevant logs:

Start at the Export messages contextual bar and its Send action described in the reproduction steps, then trace how the email export is queued. Reproduce repeated clicks and verify that only one export email is queued and the contextual bar closes after successful queuing.