review for 7035161: assert(!o->is_null_object()) failed: null object not yet handled here.

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/7035161

7035161: assert(!o->is_null_object()) failed: null object not yet handled here.
Reviewed-by:

There's a bare oop across the call to ciField::type which might cause
a safepoint resulting in the field being read from a stale oop.
Tested with crashing test nsk.stress.jck12a.jck12a006.jck12a006.