Avoid accessing layout tables at face destruction

"Fixes" https://bugs.freedesktop.org/show_bug.cgi?id=86300

Based on discussion someone else who had a similar issue, most probably
the user is releasing FT_Face before destructing hb_face_t / hb_font_t.
While that's a client bug, and while we can (and should) use FreeType
refcounting to help avoid that, it happens that we were accessing
the table when we didn't really have to.  Avoid that.

src/hb-ot-layout-private.hh

@@ -126,8 +126,7 @@ struct hb_ot_layout_lookup_accelerator_t
     lookup.add_coverage (&digest);
   }
 
-  template <typename TLookup>
-  inline void fini (const TLookup &lookup HB_UNUSED)
+  inline void fini (void)
   {
   }
 

src/hb-ot-layout.cc

@@ -84,9 +84,9 @@ void
 _hb_ot_layout_destroy (hb_ot_layout_t *layout)
 {
   for (unsigned int i = 0; i < layout->gsub_lookup_count; i++)
-    layout->gsub_accels[i].fini (layout->gsub->get_lookup (i));
+    layout->gsub_accels[i].fini ();
   for (unsigned int i = 0; i < layout->gpos_lookup_count; i++)
-    layout->gpos_accels[i].fini (layout->gpos->get_lookup (i));
+    layout->gpos_accels[i].fini ();
 
   free (layout->gsub_accels);
   free (layout->gpos_accels);

src/hb-ot-shape-complex-arabic-fallback.hh

@@ -327,7 +327,7 @@ arabic_fallback_plan_destroy (arabic_fallback_plan_t *fallback_plan)
   for (unsigned int i = 0; i < fallback_plan->num_lookups; i++)
     if (fallback_plan->lookup_array[i])
     {
-      fallback_plan->accel_array[i].fini (fallback_plan->lookup_array[i]);
+      fallback_plan->accel_array[i].fini ();
       if (fallback_plan->free_lookups)
 	free (fallback_plan->lookup_array[i]);
     }