Fix q_remove_tail and q_remove_head

Fixed the error at q_remove_tail and q_remove_head.The previous function
check whether input of character pointer is empty at the start of the
function.However this will cause the function not remove the node
when input is setting wrong.Therefore, I move the checking after the
list delete function.

Change-Id: I93e0ab7530a1cc6dbecfed444ac2e714eb7cef29

Author: charliechiou

queue.c

@@ -90,13 +90,17 @@ bool q_insert_tail(struct list_head *head, char *s)
 /* Remove an element from head of queue */
 element_t *q_remove_head(struct list_head *head, char *sp, size_t bufsize)
 {
-    if (!head || list_empty(head) || !sp) {
+    if (!head || list_empty(head)) {
         return NULL;
     }
 
     element_t *first = list_first_entry(head, element_t, list);
     list_del(&first->list);
 
+    if (!sp) {
+        return NULL;
+    }
+
     size_t len = strlen(first->value);
     size_t copy_size = (len < bufsize - 1) ? len : (bufsize - 1);
 
@@ -109,13 +113,17 @@ element_t *q_remove_head(struct list_head *head, char *sp, size_t bufsize)
 /* Remove an element from tail of queue */
 element_t *q_remove_tail(struct list_head *head, char *sp, size_t bufsize)
 {
-    if (!head || list_empty(head) || !sp) {
+    if (!head || list_empty(head)) {
         return NULL;
     }
 
     element_t *tail = list_last_entry(head, element_t, list);
     list_del(&tail->list);
 
+    if (!sp) {
+        return NULL;
+    }
+
     size_t len = strlen(tail->value);
     size_t copy_size = (len < bufsize - 1) ? len : (bufsize - 1);