[Bugfix] Support both list and generator mode & fix unnecessary error log (#599)

Signed-off-by: Gaohan123 <hgaoaf@connect.ust.hk>
Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/user_guide/examples/offline_inference/text_to_image.md

@@ -19,7 +19,7 @@ if __name__ == "__main__":
     omni = Omni(model="Qwen/Qwen-Image")
     prompt = "a cup of coffee on the table"
     outputs = omni.generate(prompt)
-    images = list(outputs)[0].request_output[0].images
+    images = outputs[0].request_output[0].images
     images[0].save("coffee.png")
 ```