fix(mm): only move model files if necessary

The old logic to check if a model needed to be moved relied on the model path being a relative path. Paths are now absolute, causing this check to fail. We then assumed the paths were different and moved the model from its current location to, well, its current location.

Use more resilient method to check if a model should be moved.

invokeai/app/services/model_install/model_install_default.py

@@ -513,10 +513,17 @@ def _sync_model_path(self, key: str) -> AnyModelConfig:
         old_path = Path(model.path)
         models_dir = self.app_config.models_path
 
-        if not old_path.is_relative_to(models_dir):
+        try:
+            old_path.relative_to(models_dir)
             return model
+        except ValueError:
+            pass
 
         new_path = models_dir / model.base.value / model.type.value / model.name
+
+        if old_path == new_path:
+            return model
+
         self._logger.info(f"Moving {model.name} to {new_path}.")
         new_path = self._move_model(old_path, new_path)
         model.path = new_path.as_posix()