[makeotf] will accept malformed MacRoman strings

[frankrolf]

In a test project, I specified the designer name of a font as ßłü.
RoboFont can generate fonts using the FDK, and can also write FDK artifacts when generating. In the resulting name table (presumably written by ufo2fdk) I get the following override:

table name {
    nameid 9 "\00DF\0142\00FC";
    nameid 9 1 "\A7\0142\9F";
} name;

Attentive readers will notice that the MacRoman string is invalid (containing a UTF-8 escape).
The problem is that makeotf generates the font without complaining.

Dumping the resulting font with ttx, we get

WARNING: Illegal XML character(s) found; replacing offending string "'ß\\x0142ü'" with '?'

    <namerecord nameID="9" platformID="1" platEncID="0" langID="0x0" unicode="True">
      ß?42ü
    </namerecord>