Commit https://github.com/Bitcoin-ABC/ElectrumABC/pull/31/commits/00cb0b018f6edbc6a4e6f2d22ddbd509e5c8681e broke the URI handling.
When the application is called with a URI as a first argument, it should start a GUI with the send tab pre-filled with the correct information. Unfortunately `argparse` does not provide a good way to default to a subparser when the provided command line argument is not one of the explicitely specified command. The previous fix was hacky because it relied on monkey-patching private variables in `argparse`, which could break in any new python release. So reverting the commit is not a good idea IMO.
Manually append the `gui` command when the first argument is a URI.
Depends on D14382