Fix PIL fp closed error on image preview (eagerly load pixel data)

app.py

@@ -140,8 +140,9 @@ def _load_image(file_path: str, page_number: int) -> tuple[int, Image.Image]:
     if path.suffix.lower() == ".pdf":
         return _render_pdf_page(path, page_number)
 
-    with Image.open(path) as img:
-        return 1, _resize_if_needed(img)
+    img = Image.open(path)
+    img.load()  # eagerly read pixel data so the fp can be released
+    return 1, _resize_if_needed(img)
 
 
 @spaces.GPU(duration=180)