[8u20] Request for approval for JDK-8034147: javac crashes with a NullPointerException during bounds checking

[Dan Smith]

Please approve this backport of a big fix from jdk9.

Bug report: https://bugs.openjdk.java.net/browse/JDK-8034147
Changeset: http://hg.openjdk.java.net/jdk9/dev/langtools/rev/9b187f24c709
jdk9 reviewers: vromero, mcimadamore

—Dan