API: Fix error points and exceptions

On /v1/model/load, some internal server errors weren't being sent,
so migrate directory checking out and also add a check to make sure
the proposed model path exists.

Signed-off-by: kingbri <bdashore3@proton.me>

main.py

@@ -1,6 +1,6 @@
 import uvicorn
 import yaml
-import pathlib
+import pathlib, os
 from auth import check_admin_key, check_api_key, load_auth_keys
 from fastapi import FastAPI, Request, HTTPException, Depends
 from fastapi.middleware.cors import CORSMiddleware
@@ -75,6 +75,8 @@ async def get_current_model():
 # Load model endpoint
 @app.post("/v1/model/load", dependencies=[Depends(check_admin_key)])
 async def load_model(data: ModelLoadRequest):
+    global model_container
+
     if model_container and model_container.model:
         raise HTTPException(400, "A model is already loaded! Please unload it first.")
 
@@ -94,13 +96,15 @@ async def load_model(data: ModelLoadRequest):
 
         load_data["draft_model_dir"] = draft_config.get("draft_model_dir") or "models"
 
+    if not model_path.exists():
+        raise HTTPException(400, "model_path does not exist. Check model_name?")
+
+    model_container = ModelContainer(model_path.resolve(), False, **load_data)
+
     def generator():
-        global model_container
-
-        model_container = ModelContainer(model_path.resolve(), False, **load_data)
         model_type = "draft" if model_container.draft_enabled else "model"
-
         load_status = model_container.load_gen(load_progress)
+
         for (module, modules) in load_status:
             if module == 0:
                 loading_bar: IncrementalBar = IncrementalBar("Modules", max = modules)