cppcheck: fix returnDanglingLifetime (l10ntools)

Change-Id: Ia3c094ee65be3f5048df6896a4a6428bdd8fed10
Reviewed-on: https://gerrit.libreoffice.org/63527
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

l10ntools/source/po.cxx

@@ -442,7 +442,7 @@ namespace
         struct tm* pNow = localtime(&aNow);
         char pBuff[50];
         strftime( pBuff, sizeof pBuff, "%Y-%m-%d %H:%M%z", pNow );
-        return pBuff;
+        return OString(pBuff);
     }
 }