fdo#64656 RTF import: handle levelnumbers without leveltext

Change-Id: I34ce7b172dc94489f7f506796e66b14598aab19c

writerfilter/qa/cppunittests/rtftok/data/pass/fdo64656.rtf

+{\rtf
+{\*\listtable 
+{\list \listtemplateid3794224 \listhybrid 
+{\listlevel \levelnfc0 \levelnfcn0 \leveljc0 \leveljcn0 \levelstartat1 \levelfollow0 \levelspace0 \levelindent0 \levellegal0 \levelnorestart0 
+{\levelnumbers ;}
+}
+{\listname ;}
+\listid258183 }
+}
+}

writerfilter/source/rtftok/rtfdocumentimpl.cxx

@@ -3843,6 +3843,7 @@ int RTFDocumentImpl::popState()
             }
             break;
         case DESTINATION_LEVELNUMBERS:
+            if (aState.aTableSprms.find(NS_ooxml::LN_CT_Lvl_lvlText))
             {
                 RTFSprms& rAttributes = aState.aTableSprms.find(NS_ooxml::LN_CT_Lvl_lvlText)->getAttributes();
                 RTFValue::Pointer_t pValue = rAttributes.find(NS_ooxml::LN_CT_LevelText_val);