758361556b
It was too easy to end up with invalid region rectangles and we were badly protected against them, so that they were hard to catch. In fact we still create a main region for the top-bar, which ended up getting a region height of -1. While this doesn't seem to have caused issues in practice, we should prevent them entirely. So idea was that at the end of region layout resolving, `BLI_rcti_is_valid()` should return `true` for the region rectangle. Further changes here ensure this is true: The `RGN_FLAG_TOO_SMALL` flag is now set whenever there is not enough space for a region or if it would get a size of zero or less. Note: Should the assert fail, please do not just disable it and try to actually address the root of the issue.