More restrict check load_combine_op. (#15479)

* fix && test=develop

* fix && test=develop

* test=develop

paddle/fluid/operators/load_combine_op.cc

@@ -64,7 +64,7 @@ class LoadCombineOp : public framework::OperatorBase {
       auto *tensor = out_var->GetMutable<framework::LoDTensor>();
 
       // Error checking
-      PADDLE_ENFORCE(static_cast<bool>(buffer), "Cannot read more");
+      PADDLE_ENFORCE(static_cast<bool>(*buffer), "Cannot read more");
 
       // Get data from fin to tensor
       DeserializeFromStream(*buffer, tensor, dev_ctx);
@@ -90,6 +90,10 @@ class LoadCombineOp : public framework::OperatorBase {
         tensor->ShareDataWith(fp16_tensor);
       }
     }
+    buffer->peek();
+    PADDLE_ENFORCE(buffer->eof(),
+                   "You are not allowed to load partial data via "
+                   "load_combine_op, use load_op instead.");
   }
 };