Fix meta tensor issue

[wkpark]

sd_models.load_model() call with already_loaded_state_dict=state_dict makes current sd_model state "meta" by line https://github.com/AUTOMATIC1111/stable-diffusion-webui/blob/v1.6.0/modules/sd_models.py#L563-L577

...
    if model_data.sd_model:
        send_model_to_trash(model_data.sd_model) # this line
        model_data.sd_model = None
        devices.torch_gc()
...

workaround this issue before calling sd_models.load_model() add the follows

diff --git a/scripts/model_mixer.py b/scripts/model_mixer.py
index 1981557..ef9a17d 100644
--- a/scripts/model_mixer.py
+++ b/scripts/model_mixer.py
@@ -2122,6 +2122,12 @@ class ModelMixerScript(scripts.Script):
             print("WARN: lowvram/medvram load_model() with minor workaround")
             sd_models.unload_model_weights()
             #sd_models.model_data.__init__()
+
+        if sd_models.model_data.sd_model:
+            sd_models.send_model_to_cpu(sd_models.model_data.sd_model) # this line.
+            sd_models.model_data.sd_model = None
+            devices.torch_gc()
+
         sd_models.load_model(checkpoint_info=checkpoint_info, already_loaded_state_dict=state_dict)
         del state_dict
         devices.torch_gc()