failed conversion of special unicode chars from UTF-8 const char* to wxString

[TomTkacz]

In the CLI, when executing write_image_file(c,file:"card.png") where c := new_card([text:"<sym>∞</sym>"]), the incorrect symbol is put onto the card image.

Displayed are the individual ASCII bytes of the symbol [0xE2 0x88 0x9E], not its unicode representation. This is despite data/magic-mana-small.mse-symbol-font/symbol-font (used in the magic-m15-altered style) listing this as the correct symbol.

I believe I tracked the issue to src/util/io/reader.cpp, where the read_utf8_line function feeds the line containing the character into a const char* buffer. When the buffer is converted to a wxString via wxString::FromUTF8, an empty string is returned.