bug of empty head of the first block

source/tensor/XMem.cpp

@@ -532,7 +532,7 @@ release a piece of memory
 */
 void XMem::Release(void * p, MTYPE size, MTYPE code)
 {
-    //if(code == signature)
+    if(code == signature)
         Release(devID, p, size);
 }
 
@@ -931,7 +931,7 @@ void XMem::RebuildIndex()
 
     for(int bi = 0; bi <= curBlockID; bi++){
         XMemBlock * block = blocks + bi;
-        if(block->mem == NULL)
+        if(block->mem == NULL || block->head == NULL)
             continue;
 
         MHeader * head = block->head;
@@ -982,7 +982,7 @@ void XMem::RebuildIndex()
                 MPieceNode * newNode = memIndex2 + nodeNumUsed2++;
                 newNode->p = p;
                 newNode->size = (char*)p + head->size - 
-                                ( head->state == 1 ? (char*)GetPitchedAddress((char*)p, MY_PITCH) : head->indexNode->pReal);
+                                ( head->state == 1 ? (char*)GetPitchedAddress((char*)p, MY_PITCH) : (char*)head->indexNode->pReal);
                 newNode->pre = NULL;
                 newNode->next = NULL;