Avoid null cgFont crash in harfBuzzCoreTextGetTable

Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp

Index: Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp
diff --git a/Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp b/Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp
index 1fc421565b0f706855be788a493cfde0c429ae2c..44257c8f4bbc816fbf45f3f09a9adec9786b8115 100644
--- a/Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp
+++ b/Source/platform/fonts/harfbuzz/HarfBuzzFaceCoreText.cpp
@@ -109,6 +109,8 @@ static void releaseTableData(void* userData)
 static hb_blob_t* harfBuzzCoreTextGetTable(hb_face_t* face, hb_tag_t tag, void* userData)
 {
     CGFontRef cgFont = reinterpret_cast<CGFontRef>(userData);
+    if (!cgFont)
+        return 0;
     CFDataRef cfData = CGFontCopyTableForTag(cgFont, tag);
     if (!cfData)
         return 0;