At least in JunitTest_sw_unoapi it happens that this downcast is called from
~SwCharFmt -> ~SwFmt -> SwClient::ModifyNotification -> SwDepend::Modify ->
SwClient::ModifyNotification -> SwEndNodeInfo::Modify, i.e., the downcasted
object is in destruction and no longer an SwCharFmt but only an SwFmt.  Whether
or not that chain of calls is actually sane---casting down to merely an SwFmt
is a quickfix at least.

Change-Id: I33f0d76c42daa2530b8d417df059de57190c5070