Fix the crash described in #5132. Patches were submitting UndoMemento…

…s to the undo system even though they ended up not being added to the scene.

The new approach is to only add them to the scene after it's clear they are going to be kept.

radiant/patch/Patch.cpp

@@ -2539,9 +2539,6 @@ void Patch::createThickenedWall(const Patch& sourcePatch,
 
 	// Notify the patch about the change
 	controlPointsChanged();
-
-	// Texture the patch "naturally"
-	NaturalTexture();
 }
 
 void Patch::stitchTextureFrom(Patch& sourcePatch) {

radiant/patch/algorithm/General.cpp

@@ -53,10 +53,6 @@ void thicken(const PatchNodePtr& sourcePatch, float thickness, bool createSeams,
 		// Now create the four walls
 		for (int i = 0; i < 4; i++)
 		{
-			// Insert each node into the same parent as the existing patch
-			// It's vital to do this first, otherwise these patches won't have valid shaders
-			parent->addChildNode(nodes[i]);
-
 			// Retrieve the contained patch from the node
 			Patch* wallPatch = Node_getPatch(nodes[i]);
 
@@ -65,15 +61,19 @@ void thicken(const PatchNodePtr& sourcePatch, float thickness, bool createSeams,
 
 			if (!wallPatch->isDegenerate())
 			{
+				// Insert each node into the same parent as the existing patch
+				// It's vital to do this first, otherwise these patches won't have valid shaders
+				parent->addChildNode(nodes[i]);
+
+				// Now the shader is realised, apply natural scale
+				wallPatch->NaturalTexture();
+
 				// Now select the newly created patch
 				Node_setSelected(nodes[i], true);
 			}
 			else
 			{
 				rMessage() << "Thicken: Discarding degenerate patch." << std::endl;
-
-				// Remove again
-				parent->removeChildNode(nodes[i]);
 			}
 		}
 	}