Coverity leak scripting.c SetGlyphName SetUnicodeValue

Any call to `SetUnicodeValue()` would leak the glyph name.

For glyphs with comments, e.g.

        Comment: "This glyph worked fine on i?86 but failed ..."

every call to native scripting `SetGlyphName()` or `SetUnicodeValue()`
would result in a leak of the old comment.

Example native source:

        glyphname = "exclam";
        Select( glyphname );
        SetGlyphName("AAA", 0);
        SetUnicodeValue(65, 0);