LibGfx: Handle UTF-16-encoded OpenType font names

This change makes OpenType::Name::string_for_id handle fonts whose names
are UTF-16-encoded (along with handling UTF-8-encoded names).

Otherwise, without this change, the existing code assumes the names are
UTF-8-encoded, fails gracelessly if they’re not, and crashes.

Fixes LadybirdBrowser/ladybird#75

(cherry picked from commit 1a9dabe5ff443315a1e3e9c577f93936e6dd45dc)

Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp

@@ -229,13 +229,23 @@ String Name::string_for_id(NameId id) const
     auto const platform_id = name_record.platform_id;
     auto const length = name_record.length;
     auto const offset = name_record.string_offset;
+    auto const name_bytes = m_string_data.slice(offset, length);
 
     if (platform_id == to_underlying(Platform::Windows)) {
         static auto& decoder = *TextCodec::decoder_for("utf-16be"sv);
-        return decoder.to_utf8(m_string_data.slice(offset, length)).release_value_but_fixme_should_propagate_errors();
+        return decoder.to_utf8(name_bytes).release_value_but_fixme_should_propagate_errors();
     }
 
-    return String::from_utf8(m_string_data.slice(offset, length)).release_value_but_fixme_should_propagate_errors();
+    auto maybe_name = String::from_utf8(name_bytes);
+    if (maybe_name.is_error()) {
+        static auto& decoder = *TextCodec::decoder_for("utf-16be"sv);
+        maybe_name = decoder.to_utf8(name_bytes);
+        if (!maybe_name.is_error())
+            return maybe_name.release_value_but_fixme_should_propagate_errors();
+        dbgln("OpenType::Name: Failed to decode name string as UTF-8 or UTF-16BE");
+        return String {};
+    }
+    return maybe_name.release_value();
 }
 
 ErrorOr<Kern> Kern::from_slice(ReadonlyBytes slice)