Add debug guard to __e_acsl_store_block_duplicate of bittree model

src/plugins/e-acsl/share/e-acsl/bittree_model/e_acsl_bittree_mmodel.c

@@ -316,13 +316,20 @@ static void delete_block(void* ptr) {
 }
 
 static void* store_block_duplicate(void* ptr, size_t size) {
+  bt_block * tmp = NULL;
   if (ptr != NULL) {
     bt_block * tmp = bt_lookup(ptr);
-    if (tmp)
-      delete_block(tmp);
+    if (tmp) {
+#ifdef E_ACSL_DEBUG
+    /* Make sure that duplicate block, if so is of the same length */
+    if (tmp->size != size)
+      vabort("Attempt to store duplicate block of different length");
+#endif
+      delete_block(ptr);
+    }
     store_block(ptr, size);
   }
-  return ptr;
+  return tmp;
 }
 
 /* }}} */