Bug 1430552 - Handle possible freetype failures in gfxFT2FontBase::GetFTGlyphAdvance to avoid risk of crashes. r=lsalzman

gfx/thebes/gfxFT2FontBase.cpp

@@ -511,14 +511,22 @@ FT_Fixed
 gfxFT2FontBase::GetFTGlyphAdvance(uint16_t aGID)
 {
     gfxFT2LockedFace face(this);
+    MOZ_ASSERT(face.get());
+    if (!face.get()) {
+        // Failed to get the FT_Face? Give up already.
+        return 0;
+    }
     int32_t flags =
         gfxPlatform::GetPlatform()->FontHintingEnabled()
             ? FT_LOAD_ADVANCE_ONLY
             : FT_LOAD_ADVANCE_ONLY | FT_LOAD_NO_AUTOHINT | FT_LOAD_NO_HINTING;
-    FT_Fixed advance = 0;
-    mozilla::DebugOnly<FT_Error> ftError =
-        FT_Load_Glyph(face.get(), aGID, flags);
+    FT_Error ftError = FT_Load_Glyph(face.get(), aGID, flags);
     MOZ_ASSERT(!ftError);
+    if (ftError != FT_Err_Ok) {
+        // FT_Face was somehow broken/invalid? Don't try to access glyph slot.
+        return 0;
+    }
+    FT_Fixed advance = 0;
     if (face.get()->face_flags & FT_FACE_FLAG_SCALABLE) {
         advance = face.get()->glyph->linearHoriAdvance;
     } else {