Use std::to_string (OOXMLParserState)

Change-Id: I145f45d9980496e1ba8636597a70c4dcbf49838c
Reviewed-on: https://gerrit.libreoffice.org/63525
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

writerfilter/source/ooxml/OOXMLParserState.cxx

@@ -82,11 +82,7 @@ void OOXMLParserState::setForwardEvents(bool bForwardEvents)
 
 const std::string OOXMLParserState::getHandle() const
 {
-    char sBuffer[256];
-
-    snprintf(sBuffer, sizeof(sBuffer), "%u", mnHandle);
-
-    return sBuffer;
+    return std::to_string(mnHandle);
 }
 
 void OOXMLParserState::setHandle()