ofz Integer overflow

Change-Id: I4ee001f2f587612f0a924e02f4f3fae4c7afbe75
Reviewed-on: https://gerrit.libreoffice.org/43844
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/sw/source/filter/ww8/ww8scan.cxx b/sw/source/filter/ww8/ww8scan.cxx
index 3a30309..3055fec 100644
--- a/sw/source/filter/ww8/ww8scan.cxx
+++ b/sw/source/filter/ww8/ww8scan.cxx
@@ -3388,7 +3388,13 @@ void WW8PLCFx_Cp_FKP::GetSprms(WW8PLCFxDesc* p)
                                    continue;
                                }
                            }
                            nLimitFC = nFcStart + nCpLen;

                            const bool bFail = o3tl::checked_add(nFcStart, nCpLen, nLimitFC);
                            if (bFail)
                            {
                                SAL_WARN("sw.ww8", "broken offset, ignoring");
                                continue;
                            }

                            //if it doesn't exist, skip it
                            if (!SeekPos(nCpStart))