Export keyboard shortcuts fails with default shortcuts

Migrated from: https://bugs.launchpad.net/inkscape/+bug/1810618

Steps to reproduce:

• Delete files in .config/inkscape/keys (or equivalent)
• Open Inkscape
• Go to preferences (Ctrl+Shift+P) > interfaces > keyboard shortcuts
• Export (bottom right)

What happened?

No file is generated. There is only an error message in the terminal:

** (inkscape:26551): WARNING **: Can't open file: /home/user/.config/inkscape/keys/default.xml (doesn't exist)

** (inkscape:26551): WARNING **: Unable to read keyboard shortcut file /home/user/.config/inkscape/keys/default.xml

What should have happened?

File should have been generated.

1. If a keyboard shortcut is made, default.xml is generated. If reset is then pressed, the desired xml file is generated.

   <?xml version="1.0" encoding="UTF-8" standalone="no"?>
<keys name="My custom shortcuts" />

2. This is also request for all default shortcuts to be exported as well.

   Note: The default shortcuts can be accessed in the keys folder listed in Preferences > System, Inkscape Data.

Inkscape Version and Operating System:

• Inkscape 0.91 (unknown) Linux Mint 18.3 Cinnamon 64 bit
• Inkscape 1.0alpha (a06af59ea3, 2019-04-13) Linux Mint 19.1