fix: build error without ENABLE_PADDLE2ONNX

Author: MistEO

fastdeploy/runtime/backends/ort/ort_backend.cc

@@ -260,8 +260,13 @@ bool OrtBackend::InitFromOnnx(const std::string& model_file,
     }
     char* model_content_ptr;
     int model_content_size = 0;
+#ifdef ENABLE_PADDLE2ONNX
     paddle2onnx::ConvertFP32ToFP16(model_file.c_str(), model_file.size(),
                                    &model_content_ptr, &model_content_size);
+#else
+    FDERROR << "Didn't compile with PaddlePaddle Frontend, FP16 is not supported" << std::endl;
+    return false;
+#endif
     std::string onnx_model_proto(model_content_ptr,
                                  model_content_ptr + model_content_size);
     delete[] model_content_ptr;