ensure that a grandparent exists when it is involved in the ballance

include/tr/tree_macros.h

@@ -267,9 +267,11 @@ typedef enum {rbBlack=1, rbRed=2} TR_rbColor;
 	while (1) {                                          \
 		TR_TREE_BALANCE_INSERT_CASE1((node))             \
 		TR_TREE_BALANCE_INSERT_CASE2((node))             \
+		if (NULL != (node)->parent->parent) {            \
 			TR_TREE_BALANCE_INSERT_CASE3((node))         \
 			TR_TREE_BALANCE_INSERT_CASE4((root), (node)) \
 			TR_TREE_BALANCE_INSERT_CASE5((root), (node)) \
+		}                                                \
 		break;                                           \
 	}