<Swing Dev> RFR [9] 8081313: MultipleDocumentHandling.java: tidy warnings

[alexander stepanov]

Hello,

Could you please review fix
http://cr.openjdk.java.net/~avstepan/8081313/webrev.00/
for
https://bugs.openjdk.java.net/browse/JDK-8081313

Just a minor fix of docs; other code is not affected.

Thanks,
Alexander