Disallow changing settings on immutable face

Ouch!

src/hb-face.cc

@@ -298,7 +298,7 @@ hb_face_get_user_data (hb_face_t          *face,
 void
 hb_face_make_immutable (hb_face_t *face)
 {
-  if (hb_object_is_inert (face))
+  if (unlikely (hb_object_is_inert (face)))
     return;
 
   face->immutable = true;
@@ -368,7 +368,7 @@ void
 hb_face_set_index (hb_face_t    *face,
 		   unsigned int  index)
 {
-  if (hb_object_is_inert (face))
+  if (face->immutable)
     return;
 
   face->index = index;
@@ -403,7 +403,7 @@ void
 hb_face_set_upem (hb_face_t    *face,
 		  unsigned int  upem)
 {
-  if (hb_object_is_inert (face))
+  if (face->immutable)
     return;
 
   face->upem = upem;
@@ -447,7 +447,7 @@ void
 hb_face_set_glyph_count (hb_face_t    *face,
 			 unsigned int  glyph_count)
 {
-  if (hb_object_is_inert (face))
+  if (face->immutable)
     return;
 
   face->num_glyphs = glyph_count;

src/hb-font.cc

@@ -357,7 +357,7 @@ hb_font_funcs_get_user_data (hb_font_funcs_t    *ffuncs,
 void
 hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
 {
-  if (hb_object_is_inert (ffuncs))
+  if (unlikely (hb_object_is_inert (ffuncs)))
     return;
 
   ffuncs->immutable = true;
@@ -1034,7 +1034,7 @@ hb_font_get_user_data (hb_font_t          *font,
 void
 hb_font_make_immutable (hb_font_t *font)
 {
-  if (hb_object_is_inert (font))
+  if (unlikely (hb_object_is_inert (font)))
     return;
 
   font->immutable = true;

src/hb-unicode.cc

@@ -310,7 +310,7 @@ hb_unicode_funcs_get_user_data (hb_unicode_funcs_t *ufuncs,
 void
 hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs)
 {
-  if (hb_object_is_inert (ufuncs))
+  if (unlikely (hb_object_is_inert (ufuncs)))
     return;
 
   ufuncs->immutable = true;