LARTC - Sep 2002 - HTB bug fix

Hello Thomasz (and LARTC),

regarding the crash-suite you send me. I located
the bug and attached patch should fix it.
Everyone who experienced crashes after "tc class change"
ahould apply and let me know.
If it will fix the issue I''ll push it into 2.4.20 before
stable one.

Detail:
"tc class change" applied to inner class overwrites internal
union members because of missing test for leaf node.

best regards,
devik

PS: thanks, Thomasz