RFR: Backport JDK-8217359: C2 compiler triggers SIGSEGV after transformation in ConvI2LNode::Ideal

[Roman Kennke]

This backports to 8u:

https://bugs.openjdk.java.net/browse/JDK-8217359

The fix applies after fixing paths and putting the patch into the right
place in connode.cpp instead of convertnode.cpp.

Testing: passes new testcase (fails without fix), passes tier1, tier2

Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8217359/webrev.00/

Can I please get a review?

Roman