make aggr safe

Author: Intron7

src/rapids_singlecell/get/_aggregated.py

@@ -9,7 +9,11 @@
 from scanpy.get._aggregated import _combine_categories
 
 from rapids_singlecell._compat import DaskArray, _meta_dense
-from rapids_singlecell._cuda import _aggr_cuda
+
+try:
+    from rapids_singlecell._cuda import _aggr_cuda
+except ImportError:
+    _aggr_cuda = None
 from rapids_singlecell.get import _check_mask
 from rapids_singlecell.preprocessing._utils import _check_gpu_X