Bug 1757897 - Add null-check for charmap in FT_Face, before trying to…

… check for symbol encoding. r=lsalzman

We need a null-check here in case FT_Select_Charmap failed to find any usable charmap in the font
(e.g. maybe an old font with only a MacRoman charmap, but no Unicode or Symbol table).

Differential Revision: https://phabricator.services.mozilla.com/D140179

gfx/thebes/gfxFT2Utils.cpp

@@ -40,7 +40,8 @@ uint32_t gfxFT2LockedFace::GetGlyph(uint32_t aCharCode) {
 #else
   uint32_t gid = FT_Get_Char_Index(mFace, aCharCode);
 #endif
-  if (!gid && mFace->charmap->encoding == FT_ENCODING_MS_SYMBOL) {
+  if (!gid && mFace->charmap &&
+      mFace->charmap->encoding == FT_ENCODING_MS_SYMBOL) {
     if (auto pua = gfxFontUtils::MapLegacySymbolFontCharToPUA(aCharCode)) {
       gid = FT_Get_Char_Index(mFace, pua);
     }