labwc-tweaks doesn't handle invalid rc.xml well

[Consolatis]

It spits out errors on the terminal but users can still select options and click Apply and there doesn't seem to be happening anything. If the user doesn't look at the terminal output (or can't because its redirected somewhere else) it looks like labwc-tweaks is simply broken and doesn't do anything.

I think labwc-tweaks should fail to start when detecting a broken (as in the XML is broken) rc.xml by showing a error dialog and then exit once confirmed.

[johanmalm]

Thanks for raising this. Yeah, I feel like I ought to have a period of focusing a bit on tweaks and get it to a stable v0.1 😄