loplugin:stringconstant: adapt to improved OUStringLiteral1 (sax)

Change-Id: Ia39a4f4689ae0d6e2b7303a89251634bfe0eeb2f

sax/source/tools/converter.cxx

@@ -820,7 +820,7 @@ bool Converter::convertDuration(double& rfTime,
                 }
                 else
                 {
-                    sDoubleStr += OUString(c);
+                    sDoubleStr += OUStringLiteral1(c);
                 }
             }
         }