add back setting ptrs to null after freeingmake

Author: dance858

src/affine/index.c

@@ -155,6 +155,7 @@ static void free_type_data(expr *node)
 {
     index_expr *idx = (index_expr *) node;
     free(idx->indices);
+    idx->indices = NULL;
 }
 
 expr *new_index(expr *child, int d1, int d2, const int *indices, int n_idxs)

src/affine/linear_op.c

@@ -55,14 +55,13 @@ static void free_type_data(expr *node)
     if (!node->jacobian)
     {
         free_csr_matrix(lin_node->A_csr);
+        lin_node->A_csr = NULL;
     }
 
     free_csc_matrix(lin_node->A_csc);
-
-    if (lin_node->b != NULL)
-    {
-        free(lin_node->b);
-    }
+    lin_node->A_csc = NULL;
+    free(lin_node->b);
+    lin_node->b = NULL;
 }
 
 static void jacobian_init(expr *node)