Avoid undef member function call with this == nullptr
Avoid undef member function call with this == nullptr

(in which case SwFrm::FindPageFrm, sw/source/core/layout/findfrm.cxx, happened
to return nullptr, so all used to go well; but still...)

Change-Id: Ib513d9a157d0135ca234930bbcbeeacf814bb80e

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core