fix a small algorythmic bug introduced during optimization.

src/tree/delete.c

@@ -123,11 +123,15 @@ TR_treeDelete(TR_Tree * this, const void * search, TR_TreeComp comp)
 			} else {
 				TR_TREE_ROTATE(right, this, node->parent);
 			}
-		} else {
-			// case 3/4
-			if (NULL != sibling
+			sibling = TR_TREE_SIBLING(node);
+		}
+
+		if (NULL == sibling
+				|| (rbBlack == sibling->color
 					&& TR_TREE_NODE_BLACK(sibling->left)
-					&& TR_TREE_NODE_BLACK(sibling->right)) {
+					&& TR_TREE_NODE_BLACK(sibling->right))) {
+			// case 3/4
+			if (NULL != sibling) {
 				sibling->color = rbRed;
 			}
 
@@ -163,6 +167,7 @@ TR_treeDelete(TR_Tree * this, const void * search, TR_TreeComp comp)
 
 				TR_TREE_ROTATE(left, this, sibling);
 			}
+			sibling = TR_TREE_SIBLING(node);
 		}
 		
 		// case 6