Fix: Brushes are erroneously destroyed in Split operations

[SamNChiet]

Issue: When more than two brush objects are selected, using a Split operation with a plane that fails to intersect one of the objects will cause the non-intersected object to be marked for deletion.

The fix is one line. In EditMode.Clip.cs, around line 647, change

if (clipSides[t] == ClipSide.CompletelyInside)
{
    // ...

to

if (clipSides[t] == ClipSide.CompletelyInside && clipMode != ClipMode.Split)
{
    // ...

Fixed!