Make TSan happy with make_immutable()

src/hb-blob.cc

diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index fca3c91..f095266 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -293,6 +293,8 @@
 {
   if (hb_object_is_inert (blob))
     return;
+  if (blob->immutable)
+    return;
 
   blob->immutable = true;
 }

src/hb-face.cc

diff --git a/src/hb-face.cc b/src/hb-face.cc
index 19eea4d..fbab18a 100644
--- a/src/hb-face.cc
+++ b/src/hb-face.cc
@@ -325,6 +325,8 @@
 {
   if (unlikely (hb_object_is_inert (face)))
     return;
+  if (face->immutable)
+    return;
 
   face->immutable = true;
 }

src/hb-font.cc

diff --git a/src/hb-font.cc b/src/hb-font.cc
index 9dcf6c1..77762f2 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -586,6 +586,8 @@
 {
   if (unlikely (hb_object_is_inert (ffuncs)))
     return;
+  if (ffuncs->immutable)
+    return;
 
   ffuncs->immutable = true;
 }
@@ -1444,6 +1446,8 @@
 {
   if (unlikely (hb_object_is_inert (font)))
     return;
+  if (font->immutable)
+    return;
 
   if (font->parent)
     hb_font_make_immutable (font->parent);

src/hb-unicode.cc

diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index bb1cd68..0e8b520 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -308,6 +308,8 @@
 {
   if (unlikely (hb_object_is_inert (ufuncs)))
     return;
+  if (ufuncs->immutable)
+    return;
 
   ufuncs->immutable = true;
 }