[10] RFR 8173181: Empty string alias in KeyStore throws StringIndexOutOfBoundsException for getEntry()

[Vincent Ryan]

Please review this fix to correct support for an empty string alias in PKCS12 
keystores.
Thanks.

Bug: https://bugs.openjdk.java.net/browse/JDK-8173181 
<https://bugs.openjdk.java.net/browse/JDK-8173181>
Webrev: http://cr.openjdk.java.net/~vinnie/8173181/webrev.00/ 
<http://cr.openjdk.java.net/~vinnie/8173181/webrev.00/>