[subset] add option --no-prune-unicode-ranges

src/hb-subset-plan.cc

diff --git a/src/hb-subset-plan.cc b/src/hb-subset-plan.cc
index f5aaaaf..195378d 100644
--- a/src/hb-subset-plan.cc
+++ b/src/hb-subset-plan.cc
@@ -403,6 +403,7 @@
   plan->name_legacy = input->name_legacy;
   plan->overlaps_flag = input->overlaps_flag;
   plan->notdef_outline = input->notdef_outline;
+  plan->prune_unicode_ranges = !input->no_prune_unicode_ranges;
   plan->retain_all_layout_features = input->retain_all_layout_features;
   plan->unicodes = hb_set_create ();
   plan->name_ids = hb_set_reference (input->name_ids);