编写合并函数，将两个有序的单链表合并成一个有序单链表，我这里的MergeList_L函数好像有点问题，能看看吗

void MergeList_L(SLNode *La,SLNode *Lb,SLNode **Lc)
{
SLNode *pa,*pb,*pc;
pa=La->next; pb=Lb->next;
*Lc= pc =La;
while (pa&&pb)
{
if (pa->data<=pb->data)
{
pc->next=pa;
pc=pa;
pa=pa->next;
}
else
{
pc->next=pb;
pc=pb;
pb=pb->next;
}
}
pc->next=pa?pa:pb;
free(Lb);
}