Don't do fractions if buffer is ASCII-only

src/hb-buffer-private.hh

diff --git a/src/hb-buffer-private.hh b/src/hb-buffer-private.hh
index 574fb36..8550517 100644
--- a/src/hb-buffer-private.hh
+++ b/src/hb-buffer-private.hh
@@ -43,8 +43,9 @@
 
 enum hb_buffer_scratch_flags_t {
   HB_BUFFER_SCRATCH_FLAG_DEFAULT			= 0x00000000u,
-  HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES		= 0x00000001u,
-  HB_BUFFER_SCRATCH_FLAG_HAS_SPACE_FALLBACK		= 0x00000002u,
+  HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII			= 0x00000001u,
+  HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES		= 0x00000002u,
+  HB_BUFFER_SCRATCH_FLAG_HAS_SPACE_FALLBACK		= 0x00000004u,
 };
 template <> class hb_mark_as_flags_t<hb_buffer_scratch_flags_t> {};
 

src/hb-ot-layout-private.hh

diff --git a/src/hb-ot-layout-private.hh b/src/hb-ot-layout-private.hh
index 60fca26..049b232 100644
--- a/src/hb-ot-layout-private.hh
+++ b/src/hb-ot-layout-private.hh
@@ -249,6 +249,7 @@
 
   if (u >= 0x80)
   {
+    buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII;
     if (unlikely (unicode->is_default_ignorable (u)))
     {
       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES;

src/hb-ot-shape.cc

diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 30563d0..be9c438 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -346,7 +346,8 @@
 static inline void
 hb_ot_shape_setup_masks_fraction (hb_ot_shape_context_t *c)
 {
-  if (!c->plan->has_frac)
+  if (!(c->buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII) ||
+      !c->plan->has_frac)
     return;
 
   hb_buffer_t *buffer = c->buffer;