Work around missing core conversion model issue

- This adds additional logic to the safetensors->diffusers conversion script
  to check for and install missing core conversion models at runtime.

- Fixes #5934

invokeai/backend/model_manager/convert_ckpt_to_diffusers.py

@@ -76,6 +76,25 @@ logger = InvokeAILogger.get_logger(__name__)
 CONVERT_MODEL_ROOT = InvokeAIAppConfig.get_config().models_path / "core/convert"
 
 
+def install_dependencies():
+    """
+    Check for, and install, missing model dependencies.
+    """
+    conversion_models = [
+        "clip-vit-large-patch14",
+        "CLIP-ViT-H-14-laion2B-s32B-b79K",
+        "stable-diffusion-2-clip",
+        "stable-diffusion-safety-checker",
+        "CLIP-ViT-bigG-14-laion2B-39B-b160k",
+        "bert-base-uncased",
+    ]
+    if any(not (CONVERT_MODEL_ROOT / x).exists() for x in conversion_models):
+        logger.warning("Installing missing core safetensor conversion models")
+        from invokeai.backend.install.invokeai_configure import download_conversion_models  # noqa
+
+        download_conversion_models()
+
+
 def shave_segments(path, n_shave_prefix_segments=1):
     """
     Removes segments. Positive values shave the first segments, negative shave the last segments.
@@ -1697,6 +1716,8 @@ def download_controlnet_from_original_ckpt(
 
 
 def convert_ldm_vae_to_diffusers(checkpoint, vae_config: DictConfig, image_size: int) -> AutoencoderKL:
+    install_dependencies()
+
     vae_config = create_vae_diffusers_config(vae_config, image_size=image_size)
 
     converted_vae_checkpoint = convert_ldm_vae_checkpoint(checkpoint, vae_config)
@@ -1717,6 +1738,7 @@ def convert_ckpt_to_diffusers(
     and in addition a path-like object indicating the location of the desired diffusers
     model to be written.
     """
+    install_dependencies()
     pipe = download_from_original_stable_diffusion_ckpt(checkpoint_path, **kwargs)
 
     # TO DO: save correct repo variant
@@ -1736,6 +1758,7 @@ def convert_controlnet_to_diffusers(
     and in addition a path-like object indicating the location of the desired diffusers
     model to be written.
     """
+    install_dependencies()
     pipe = download_controlnet_from_original_ckpt(checkpoint_path, **kwargs)
 
     # TO DO: save correct repo variant