PVS-Studio warning V547 for shp2xml

char *chkXml(char *buf) {
 for (char *s = buf; *s; s++)
   if (*s == '&') *s = '/';
   ....
   else if (*s > 127) *s = '~';
 return buf;
}

This suspicious code was found in shp2xml project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression '* s > 127' is always false. The value range of signed char type: [-128, 127]. Shp2Xml shp2xml.cpp 18

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