[10] RFR(XS) 8194989: 2 Null pointer dereference defect groups caused by Dependencies::DepValue::as_klass()

[dean.long at oracle.com]

http://cr.openjdk.java.net/~dlong/8194989/webrev/

https://bugs.openjdk.java.net/browse/JDK-8194989


Added an assert to fix a possible null pointer dereference in as_klass, 
then did the same for as_method because it uses the same pattern.


dl