8288302: Shenandoah: SIGSEGV in vm maybe related to jit compiling xerces

Backport-of: 5977ce5adf85c2fb9b1dd62ed250f6d4f05a613c

Author: rwestrel

src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp

@@ -1006,7 +1006,8 @@ Node* ShenandoahBarrierSetC2::ideal_node(PhaseGVN* phase, Node* n, bool can_resh
   } else if (can_reshape &&
              n->Opcode() == Op_If &&
              ShenandoahBarrierC2Support::is_heap_stable_test(n) &&
-             n->in(0) != NULL) {
+             n->in(0) != NULL &&
+             n->outcnt() == 2) {
     Node* dom = n->in(0);
     Node* prev_dom = n;
     int op = n->Opcode();