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 a leak of the old comment.

Example native source:
        glyphname = "exclam";
        Select( glyphname );
        SetGlyphName("AAA", 0);
        SetUnicodeValue(65, 0);
Merge pull request #1657 from tshinnic/coverity_leak_scripting_setglyphname

Coverity leak scripting.c SetGlyphName SetUnicodeValue