Fix regression induced (but likely not caused) by commit e91e5fed

Commiting on behalf of Jaime Torres.

Ratio:
On k-c-d I suggested this would be another ouotcome of bug #213068 and Jaime could confirm this and the
scrollbar policy workaround to work.
He suggested to fix it by "setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);" instead (since presumingly the
pluginselector is always top-down oriented)
I tested that variant as well and could not reproduce the issue.

Since Jaime has no acces to his development environment for today he asked me to either revert his commit or
apply the hotfix working around bug #213068 as mentioned above.

Because i could not spot any bug in his commit i'll go with the hotfix to prevent a regression.
Resolving the actual recursion bug is an outstanding issue.

CCBUG: 213068
CCBUG: 287847