Fix gather op bug (#19168)

* fix gather op bug
test=develop

paddle/fluid/operators/gather.cu.h

@@ -49,10 +49,16 @@ __global__ void GatherCUDAKernel(const T* params, const IndexT* indices,
 template <typename T, typename IndexT = int>
 void GPUGather(const platform::DeviceContext& ctx, const Tensor& src,
                const Tensor& index, Tensor* output) {
-  // PADDLE_ENFORCE(platform::is_gpu_place(place));
   // check index of shape 1-D
-  PADDLE_ENFORCE(index.dims().size() == 1 ||
-                 (index.dims().size() == 2 && index.dims()[1] == 1));
+  if (index.dims().size() == 1) {
+    PADDLE_ENFORCE_GT(index.dims()[0], 0,
+                      "The index of gather_op should not be empty when the "
+                      "index's rank is 1.");
+  } else if (index.dims().size() == 2) {
+    PADDLE_ENFORCE_EQ(index.dims()[1], 1,
+                      " If the index's rank of gather_op is 2, the second "
+                      "dimension should be 1.");
+  }
 
   int index_size = index.dims()[0];