C#: Fix NPE in CSharpReceiver when receiving new DirectiveLine elements

The receiveList protocol creates objenesis instances (with null fields)
for new ADD elements, so dl.getKind() can be null even when dl is not.
Added null check for getKind() to match the existing dl != null guard.

Author: knutwannheden

rewrite-csharp/src/main/java/org/openrewrite/csharp/rpc/CSharpReceiver.java

@@ -715,7 +715,7 @@ public J visitConditionalDirective(Cs.ConditionalDirective conditionalDirective,
         List<Cs.DirectiveLine> directiveLines = q.receiveList(conditionalDirective.getDirectiveLines(), dl -> {
             int lineNumber = q.receive(dl != null ? dl.getLineNumber() : 0);
             String text = q.receive(dl != null ? dl.getText() : "");
-            Cs.PreprocessorDirectiveKind kind = Cs.PreprocessorDirectiveKind.values()[q.receive(dl != null ? dl.getKind().ordinal() : 0)];
+            Cs.PreprocessorDirectiveKind kind = Cs.PreprocessorDirectiveKind.values()[q.receive(dl != null && dl.getKind() != null ? dl.getKind().ordinal() : 0)];
             int groupId = q.receive(dl != null ? dl.getGroupId() : 0);
             int activeBranchIndex = q.receive(dl != null ? dl.getActiveBranchIndex() : -1);
             return new Cs.DirectiveLine(lineNumber, text, kind, groupId, activeBranchIndex);