[subset] always generate AdvMap (#5524)

src/hb-ot-var-hvar-table.hh

diff --git a/src/hb-ot-var-hvar-table.hh b/src/hb-ot-var-hvar-table.hh
index 6d57690..ce1f9dc 100644
--- a/src/hb-ot-var-hvar-table.hh
+++ b/src/hb-ot-var-hvar-table.hh
@@ -118,7 +118,6 @@
 	      const hb_vector_t<hb_inc_bimap_t> &inner_maps,
 	      const hb_subset_plan_t *plan)
   {
-    if (!input_map) return;
     outer_bit_count = 1;
     inner_bit_count = 1;