[Bugfix] Always apply MM processor even when no MM items are passed (#26240)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/model_executor/models/phi3v.py

@@ -507,8 +507,8 @@ class Phi3VMultiModalProcessor(BaseMultiModalProcessor[Phi3VProcessingInfo]):
         )
 
         # Keep the behavior in line with HF processor
-        if token_ids[:2] == tokenizer.encode("<s> <|image|>",
-                                             add_special_tokens=False):
+        if len(mm_prompt_updates) and (token_ids[:2] == tokenizer.encode(
+                "<s> <|image|>", add_special_tokens=False)):
             token_ids = [token_ids[0], *token_ids[2:]]
             placeholders = {
                 modality: [