Handle when with a DNode just like a normal expression in IR.

This is a gross fix, and we need to reexamine this code.

It will be a fix for #2423 in the interim.

Author: headius

core/src/main/java/org/jruby/ir/IRBuilder.java

@@ -1034,7 +1034,14 @@ public Operand buildCase(CaseNode caseNode, IRScope s) {
             Variable eqqResult = s.createTemporaryVariable();
             labels.add(bodyLabel);
             Operand v1, v2;
-            if (whenNode.getExpressionNodes() instanceof ListNode) {
+            if (whenNode.getExpressionNodes() instanceof DNode) {
+                // DNode produces a proper result, so we don't want the special ListNode handling below
+                // FIXME: This is obviously gross, and we need a better way to filter out non-expression ListNode here
+                // See GH #2423
+                s.addInstr(new EQQInstr(eqqResult, build(whenNode.getExpressionNodes(), s), value));
+                v1 = eqqResult;
+                v2 = manager.getTrue();
+            } else if (whenNode.getExpressionNodes() instanceof ListNode) {
                 // Note about refactoring:
                 // - BEQInstr has a quick implementation when the second operand is a boolean literal
                 //   If it can be fixed to do this even on the first operand, we can switch around