RFR: NPE for some illegal input

[bitter_fox]

Hi, Robert.

>From new commit, some illegal input make NPE:
-> )
...
Exception in thread "main" java.lang.NullPointerException
    at tool.Repl.printDiagnostics(Repl.java:282)
    at tool.Repl.processSource(Repl.java:361)
    at tool.Repl.run(Repl.java:166)
    at tool.Repl.start(Repl.java:142)
    at tool.Repl.main(Repl.java:128)

or ->, [], ::, etc...

Please review my patch:
webrev: http://cr.openjdk.java.net/~shinyafox/kulla/1/webrev.00/

Regards,
shinyafox
ShinyaYoshida(@bitter_fox)