[gsubgpos] Skippy-iter: Prefer correctness to performance

Prefer unsafe-to-concat correctness, over performance.

src/hb-ot-layout-gsubgpos.hh

diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index cd011b0..561c727 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -535,7 +535,7 @@
     bool next (unsigned *unsafe_to = nullptr)
     {
       assert (num_items > 0);
-      while (idx + num_items < end)
+      while (idx + 1/*num_items*/ < end)
       {
 	idx++;
 	hb_glyph_info_t &info = c->buffer->info[idx];
@@ -568,7 +568,7 @@
     bool prev (unsigned *unsafe_from = nullptr)
     {
       assert (num_items > 0);
-      while (idx > num_items - 1)
+      while (idx > 0/*num_items - 1*/)
       {
 	idx--;
 	hb_glyph_info_t &info = c->buffer->out_info[idx];