fix path bug visium hd

Author: LucaMarconato

src/spatialdata_io/readers/visium_hd.py

@@ -272,6 +272,8 @@ def _get_bins(path: Path) -> list[str]:
             fullres_image_paths = [path_fullres / image_filename for image_filename in fullres_image_filenames]
         elif list((path_fullres := (path / f"{filename_prefix}tissue_image")).parent.glob(f"{path_fullres.name}.*")):
             fullres_image_paths = list(path_fullres.parent.glob(f"{path_fullres.name}.*"))
+        else:
+            fullres_image_paths = []
         if len(fullres_image_paths) > 1:
             warnings.warn(
                 f"Multiple files found in {path_fullres}, using the first one: {fullres_image_paths[0].stem}. Please"