fix concat axis bug (#50951)

* fix concat bug

* recommit for ci

paddle/fluid/inference/tensorrt/convert/concat_op.cc

@@ -45,10 +45,11 @@ class ConcatOpConverter : public OpConverter {
       itensors.push_back(engine_->GetITensor(input_name));
     }
     int axis = PADDLE_GET_CONST(int, op_desc.GetAttr("axis"));
-    if (axis == -1) {
-      axis = (engine_->GetITensor(op_desc.Input("X").front())->getDimensions())
-                 .nbDims -
-             1;
+    if (axis < 0) {
+      axis = engine_->GetITensor(op_desc.Input("X").front())
+                 ->getDimensions()
+                 .nbDims +
+             axis;
     } else {
       if (!engine_->with_dynamic_shape()) {
         axis = axis - 1;  // Remove batch dim