Prevent resizes when folder space calculation progress becomes visible or hidden

I’ve noticed some flickering when a folder is selected/unselected – the size statistics under the panel briefly become larger. This is particularly noticeable in Brief View, for a split second the last item of the column is pushed out to the next column because there isn’t enough vertical space left for it.

I checked and the issue is that the statistics consist out of three widgets. The totals widget is always visible and has height 20 for me. The other two widgets only become visible when folder size is being calculated: quickSizeCalcProgress with height 26 and cancelQuickSizeCalcButton with height 32. These two widgets being so much larger, they cause a resize whenever they are being shown/hidden.

The proper solution here should be reserving sufficient vertical space up front. Not sure whether I found the best approach for that.