fix path in stack step

preprocessor/preprocessor/steps/stack.py

@@ -12,8 +12,7 @@ from ..util import replace_ext
 def stack_bands_step(source_dir: os.PathLike, target_dir: os.PathLike, group_by: str=None, sort_by: str=None, order: List[str]=None):
     """ Stack bands of the individual images
     """
-    filenames = glob(join(source_dir, '*/*.tif'), recursive=True)
-
+    filenames = glob(join(source_dir, '*.tif'), recursive=True)
     # check if we have a group_by regex. If yes, use the first
     # re-group to group by.
     # Fallback is basename of file as groupname