RFR(T): 8252296: Shenandoah: crash in CallNode::extract_projections

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8252296/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8252296

My fix for 8251527 has caused failures with shenandoah enabled because
CallNode::extract_projections() is called with a graph in the process of
being modified where a ProjNode has more than one control use.

Roland.