Don't unload/reload model from CPU uselessly.

comfy/model_management.py

@@ -0,0 +1,26 @@
+
+
+current_loaded_model = None
+
+
+def unload_model():
+    global current_loaded_model
+    if current_loaded_model is not None:
+        current_loaded_model.model.cpu()
+        current_loaded_model.unpatch_model()
+        current_loaded_model = None
+
+
+def load_model_gpu(model):
+    global current_loaded_model
+    if model is current_loaded_model:
+        return
+    unload_model()
+    try:
+        real_model = model.patch_model()
+    except Exception as e:
+        model.unpatch_model()
+        raise e
+    current_loaded_model = model
+    real_model.cuda()
+    return current_loaded_model