Fix PixelSmith proceeding on unsupported model types

The unsupported-model warning fell through and switched non-SDXL models
into PixelSmithXLPipeline with an SDXL VAE, corrupting the pipeline.
Return early like every sibling script does after this check.

https: //claude.ai/code/session_014QWKWgKvMevcuvfCnsYoT2
Co-Authored-By: Claude <noreply@anthropic.com>

scripts/pixelsmith_ext.py

@@ -46,6 +46,7 @@ class PixelSmithScript(scripts_manager.Script):
         supported_model_list = ['sdxl']
         if shared.sd_model_type not in supported_model_list:
             log.warning(f'PixelSmith: class={shared.sd_model.__class__.__name__} model={shared.sd_model_type} required={supported_model_list}')
+            return None
         from scripts.pixelsmith import PixelSmithXLPipeline, PixelSmithVAE # pylint: disable=no-name-in-module
         self.orig_pipe = shared.sd_model
         self.orig_vae = shared.sd_model.vae