Round the corners of the splash screen image according to the theme's User Interface > Menu Back > Roundness preference. Previously the rounding was added to the image itself, which was fiddly to do. The rounded corners of the popup background would not match the one of the image if the preference was changed. The current splash image will likely be updated to not include rounded corners in a separate commit. Differential Revision: https://developer.blender.org/D6847 Reviewed by: Julian Eisel (with some changes)