Set node type when nil-ing an id node.

- Nodes can't stay as type AST_ExprID if they don't also have the
  operation PEX_ID.

src/zscript/zcc_compile.cpp

@@ -352,6 +352,7 @@ ZCC_Expression *ZCCCompiler::IdentifyIdentifier(ZCC_ExprID *idnode)
 	// Identifier didn't refer to anything good, so type error it.
 	idnode->Type = TypeError;
 	idnode->Operation = PEX_Nil;
+	idnode->NodeType = AST_Expression;
 	return idnode;
 }