fix the div 0 error of sequence_concat (#49963)

* fix the div 0 error of sequence_concat
* Update test_sequence_concat.py

paddle/fluid/operators/sequence_ops/sequence_concat_op.cc

@@ -69,6 +69,11 @@ class SequenceConcatOp : public framework::OperatorWithKernel {
         out_dims = phi::vectorize(x_dim);
       }
       batch_size += x_dim[0];
+      PADDLE_ENFORCE_NE(
+          x_dim[0],
+          0,
+          platform::errors::InvalidArgument(
+              "The first dim of SequenceConcatOp inputs must not be 0."));
       if (feature_size == 0) {
         feature_size = phi::product(x_dim) / x_dim[0];
       } else {

python/paddle/fluid/tests/unittests/sequence/test_sequence_concat.py

@@ -134,6 +134,15 @@ class TestSequenceConcatOpError(unittest.TestCase):
 
         self.assertRaises(TypeError, test_dtype)
 
+        def test_0_shape():
+            # dtype must be 'float32', 'float64', 'int64'
+            x4_data = paddle.static.data(name="x4", shape=[0], dtype='float32')
+            y4_data = paddle.static.data(name="y4", shape=[1], dtype='float32')
+            input_list = [x4_data, y4_data]
+            paddle.static.nn.sequence_lod.sequence_concat(input=input_list)
+
+        self.assertRaises(ValueError, test_0_shape)
+
 
 if __name__ == '__main__':
     paddle.enable_static()