RtfAttributeOutput::FlyFrameGraphic: don't try to compare a null pointer

sw/source/filter/ww8/rtfattributeoutput.cxx

@@ -3453,7 +3453,7 @@ void RtfAttributeOutput::FlyFrameGraphic( const SwFlyFrmFmt* pFlyFrmFmt, const S
        the wmf format wrapped in nonshppict, so as to keep wordpad happy. If its
        a wmf already then we don't need any such wrapping
        */
-    bool bIsWMF = std::strcmp(pBLIPType, OOO_STRING_SVTOOLS_RTF_WMETAFILE) == 0;
+    bool bIsWMF = pBLIPType && std::strcmp(pBLIPType, OOO_STRING_SVTOOLS_RTF_WMETAFILE) == 0;
     if (!bIsWMF)
         m_rExport.Strm() << "{" OOO_STRING_SVTOOLS_RTF_IGNORE OOO_STRING_SVTOOLS_RTF_SHPPICT;