RFR JDK-8129544: ArrayIndexOutOfBoundsException when decoding corrupt Base64 string

[Xueming Shen]

Hi,

Please help review the change for JDK-8129544.

Issue:     https://bugs.openjdk.java.net/browse/JDK-8129544
Webrev: http://cr.openjdk.java.net/~sherman/8129544

Thanks,
-Sherman