Escape ampersands in URLs

... otherwise civitai URLs ruin the process :(

app.py

@@ -11,14 +11,14 @@ def download_ckpt(ckpt_url):
     if "drive.google.com" in ckpt_url:
         gdown.download(url=ckpt_url, output="model.ckpt", quiet=False, fuzzy=True)
     else:
-        os.system(f"wget {ckpt_url} -O model.ckpt")
+        os.system(f"wget '{ckpt_url}' -O model.ckpt")
     return "download ckpt done!"
 
 def download_vae(vae_url):
     if "drive.google.com" in vae_url:
         gdown.download(url=vae_url, output="vae.ckpt", quiet=False, fuzzy=True)
     else:
-        os.system(f"wget {vae_url} -O vae.ckpt")
+        os.system(f"wget '{vae_url}' -O vae.ckpt")
     return "download vae done!"
 
 def to_pt():