Commit 1:
GUI: If BIP70 is disabled, attempt to fall back to BIP21 parsing
GUI: If BIP70 is disabled, attempt to fall back to BIP21 parsing
Commit 2:
GUI: If BIP70 is disabled, give a proper error when trying to open a payment request file
https://github.com/bitcoin/bitcoin/pull/15063/commits/113f0004bec2dd203502f2a9bcba93676d5b9cda
This is a backport of core#15063