RFR (XS) : 8031191 Warning exception when XMLSignature logging is enabled

[Seán Coffey]

Simple fix to the issue reported in the bug report. I've moved the 
logging calls past the 'sa.initVerify(pk);" call.

bug : https://bugs.openjdk.java.net/browse/JDK-8031191
webrev : http://cr.openjdk.java.net/~coffeys/webrev.8031191/webrev/

regards,
Sean.