In the node space context update function: Properly clear the snode->edittree pointer when no snode->nodetree is active. This would lead to crash in operators when switching from an existing node tree, since the usual poll function only tests for the edittree.

Fixes bug #29566.

source/blender/editors/space_node/node_edit.c

@@ -483,6 +483,7 @@ void node_tree_from_ID(ID *id, bNodeTree **ntree, bNodeTree **edittree, int *tre
 	}
 	else {
 		*ntree= NULL;
+		*edittree= NULL;
 		if(treetype) *treetype= 0;
 	}
 }