fdo#49692 fix RTF export of empty paragraph numbering rules

When there is a numbering rule, the fallback text is constructed so that
whitespace separates the numbering and the paragraph text. When the
numbering is empty, we don't need that separator.

Change-Id: I17a11ddd73addc8c95a0c2b54402e6dd2705d094

sw/source/filter/ww8/rtfattributeoutput.cxx

@@ -2513,10 +2513,9 @@ void RtfAttributeOutput::ParaNumRule_Impl( const SwTxtNode* pTxtNd, sal_Int32 nL
             else
                 sTxt = pTxtNd->GetNumString();
 
-            m_aStyles.append(' ');
-
             if (sTxt.Len())
             {
+                m_aStyles.append(' ');
                 m_aStyles.append(m_rExport.OutString(sTxt, m_rExport.eDefaultEncoding));
             }
 
@@ -2524,7 +2523,8 @@ void RtfAttributeOutput::ParaNumRule_Impl( const SwTxtNode* pTxtNd, sal_Int32 nL
             {
                 if( OUTLINE_RULE != pRule->GetRuleType() )
                 {
-                    m_aStyles.append(OOO_STRING_SVTOOLS_RTF_TAB);
+                    if (sTxt.Len())
+                        m_aStyles.append(OOO_STRING_SVTOOLS_RTF_TAB);
                     m_aStyles.append('}');
                     m_aStyles.append(OOO_STRING_SVTOOLS_RTF_ILVL);
                     if( nLvl > 8 )            // RTF knows only 9 levels