don't crash on formatting outline level 10 in master view

There are only 9 outline level styles, but we are allowed
(for some nutball reason) to create 10 levels, trying
to change the format of level 10 will then crash when
trying to apply its formatting to the non-existent
underlying style

Change-Id: Ic240322f98d832bc59edb502dd6d4988aa022481