[Bugfix] Fix phi3v incorrect image_idx when using async engine (#7916)

vllm/model_executor/models/phi3v.py

@@ -422,7 +422,9 @@ def input_processor_for_phi3v(ctx: InputContext, llm_inputs: LLMInputs):
 
     prompt = llm_inputs.get("prompt")
     if prompt is None:
-        image_idx = []
+        # for async server request, we assume prompt and its token_ids is always
+        # in correct format. And num_image_tags == len(image_data) always True.
+        image_idx = range(1, len(image_data) + 1)
         new_prompt = None
     else:
         image_idx = sorted(map(int, re.findall(r"<\|image_(\d+)\|>+", prompt)))