Wallet can pay multiple of same bip70 invoice simultaneously #4171

Describe the issue

When you click a DASH:URI you can load the same transaction multiple times into the wallet, even if it is a bip70 invoice.

Also the QT wallet doesn't respect   spaces but mobile wallets do.

Can you reliably reproduce the issue?

If so, please list the steps to reproduce below:

1. Click on a bip70 invoice multiple times with a dash: URI (see video)

Expected behaviour

First transaction should load into wallet and no further transactions. You shouldn't be able to settle the same BIP70 invoice multiple times.

Actual behaviour

Each click results in an additional transaction being loaded.

Screenshots

See video

What version of Dash Core are you using?

Official binary:
/Dash Core:0.16.1.1/

Video: https://www.youtube.com/watch?v=BYmmjObOaTA