[10] RFR(S) 8194992: Null pointer dereference in MultiNode::proj_out related to loopexit()

[dean.long at oracle.com]

http://cr.openjdk.java.net/~dlong/8194992/webrev/

https://bugs.openjdk.java.net/browse/JDK-8194992


This fix is uses the same approach as 8194988.  I split loopexit() into 
loopexit_or_null(), which can return NULL, and loopexit() which cannot.


dl