[BugFix] Fix indexing with ghostlayers

The Block indexing has bug when created with an iteration slice and ghost layers. With !341 (merged) The Block indexing supports slices more naturally by limiting the iteration space to the sliced size. Thus the counter index is multiplied by the step size. This was done also for the offset of the ghostlayers which is wrong.

This MR fixes the problem

pystencils/gpu/kernelcreation.py

@@ -133,6 +133,11 @@ def created_indexed_cuda_kernel(assignments: NodeCollection, config: CreateKerne
     assignments = assignments.all_assignments
     assignments = add_types(assignments, config)
 
+    for index_field in index_fields:
+        index_field.field_type = FieldType.INDEXED
+        assert FieldType.is_indexed(index_field)
+        assert index_field.spatial_dimensions == 1, "Index fields have to be 1D"
+
     def get_coordinate_symbol_assignment(name):
         for ind_f in index_fields:
             assert isinstance(ind_f.dtype, StructType), "Index fields have to have a struct data type"