[REVIEW 3-5] fix RTF export table output for subtables

[Miklos Vajna]

Hi,

See
http://cgit.freedesktop.org/libreoffice/core/commit/?id=1f77a5e8d5bf8a7f1b7bd7206996d2b2efc59462

It makes the RTF export generate valid table output in case the original
ODT had table:is-sub-table elements.

Could somebody sign-off and push to -3-5, please?

Thanks,

Miklos