Initial '0' on app startup

Hello, Old versions of GNOME Calculator start with an empty input box, but recently a 0 has appeared on startup.

This is causing OpenQA test gnome_calculator to fail: https://openqa.gnome.org/tests/554#step/app_gnome_calculator/2

Is the change intentional? If so, I'll update the test. If not, then either Calculator itself has a bug, or things somehow changed in GNOME OS.