[Core] More fixes to MultiModalEmbeddings type handling (#19715)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

vllm/model_executor/models/glm4v.py

@@ -609,7 +609,8 @@ class GLM4VForCausalLM(ChatGLMBaseModel, SupportsLoRA, SupportsPP,
     ) -> torch.Tensor:
         inputs_embeds = self.transformer.get_input_embeddings(input_ids)
 
-        if multimodal_embeddings is not None:
+        if multimodal_embeddings is not None \
+            and len(multimodal_embeddings) != 0:
             inputs_embeds = merge_multimodal_embeddings(
                 input_ids=input_ids,
                 inputs_embeds=inputs_embeds,