Build and Preview work without selecting a preset

[HeyMyian]

After adding and deleting build presets, the selection of the builds in this window vanishes. The "Preview" and "Build" functions still work. I think they use the first preset in the list. I noticed this because when closing and reopening this window, when no build is selected, the preview is always empty and has to be re-generated.

It looks like, code-wise, the selection simply needs to be explicitly re-applied to the previous or next entry after a build has been deleted. Or in the case of adding a build, the new build should be selected. The state that no build is selected shouldn't be possible.

(2.6b2)