corrected error handling

app.py

@@ -92,13 +92,13 @@ def button_click(hf_model_id, conv_template, quantization, oauth_token: gr.OAuth
     convert_weight_result = subprocess.run(["mlc_llm convert_weight ./dist/models/" + model_dir_name + "/" + \
               " --quantization " + quantization + \
               " -o dist/" + mlc_model_name], shell=True, capture_output=True, text=True)
-    if convert_weight_result.stderr:
+    if convert_weight_result.returncode != 0:
         return convert_weight_result.stderr
     
     gen_config_result = subprocess.run(["mlc_llm gen_config ./dist/models/" + model_dir_name + "/" + \
               " --quantization " + quantization + " --conv-template " + conv_template + \
               " -o dist/" + mlc_model_name + "/"], shell=True, capture_output=True, text=True)
-    if gen_config_result.stderr:
+    if gen_config_result.returncode != 0:
         return gen_config_result.stderr
     
     # push to HF