Fix double free error

Removed the free(old) call from the _twin_queue_delete function,
consolidating memory deallocation into the _twin_queue_review_order
 function. This change improves memory management and enhances the
maintainability of the code.

The fix was verified on the fbdev backend using GDB to confirm that
 old is properly freed during the execution of free(q) in the
_twin_queue_review_order function. Additionally, on the same
backend, AddressSanitizer was used to confirm the absence of memory
 leaks and double free issues.

Close #75

Author: huaxinliao

include/twin_private.h

@@ -453,7 +453,6 @@ void _twin_path_sfinish(twin_path_t *path);
 typedef struct _twin_queue {
     struct _twin_queue *next;
     struct _twin_queue *order;
-    bool walking;
     bool deleted;
 } twin_queue_t;
 

src/queue.c

@@ -19,7 +19,6 @@ void _twin_queue_insert(twin_queue_t **head,
             break;
     new->next = *prev;
     new->order = 0;
-    new->walking = false;
     new->deleted = false;
     *prev = new;
 }
@@ -54,8 +53,6 @@ void _twin_queue_delete(twin_queue_t **head, twin_queue_t *old)
 {
     _twin_queue_remove(head, old);
     old->deleted = true;
-    if (!old->walking)
-        free(old);
 }
 
 twin_queue_t *_twin_queue_set_order(twin_queue_t **head)
@@ -64,7 +61,6 @@ twin_queue_t *_twin_queue_set_order(twin_queue_t **head)
 
     for (twin_queue_t *q = first; q; q = q->next) {
         q->order = q->next;
-        q->walking = true;
     }
     return first;
 }
@@ -76,7 +72,6 @@ void _twin_queue_review_order(twin_queue_t *first)
     for (q = first; q; q = o) {
         o = q->order;
         q->order = 0;
-        q->walking = false;
         if (q->deleted)
             free(q);
     }