[Libreoffice] [REVIEW] Fix crash from forms.OGridControlModel unoapitests

[Tor Lillqvist]

Seems to be fixed already in a different way in -3-4 (and presumably -3-4-0) by Kohei in 06b6df6759929073e917ae0fa7e819407d3e2555 , "fdo#36288: Fixed a crasher on Base" on Apr 20. Why the crash still happens then, no idea. Anyway, cherry-pick fails.

I guess a merge of -3-4 to master is long overdue...

--tml