Avoid DtoH sync from access of nonzero() item in scheduler (#11696)

src/diffusers/pipelines/flux/pipeline_flux.py

@@ -898,6 +898,7 @@ class FluxPipeline(
             )
 
         # 6. Denoising loop
+        self.scheduler.set_begin_index(0)
         with self.progress_bar(total=num_inference_steps) as progress_bar:
             for i, t in enumerate(timesteps):
                 if self.interrupt: