MqTree: Fix debugging output macro for disabled debugging

Fixes:

      CC       src/marquee-tree.o
    src/tree.c: In function ‘mq_tree_append_child_allocated’:
    src/tree.c:171:41: error: macro "debug_print_tree" passed 2 arguments, but takes just 1
      debug_print_tree("Appended child", node);
                                             ^
    src/tree.c:171:2: error: ‘debug_print_tree’ undeclared (first use in this function)
      debug_print_tree("Appended child", node);
      ^
    src/tree.c:171:2: note: each undeclared identifier is reported only once for each function it appears in
    src/tree.c: In function ‘mq_tree_append_sibling_allocated’:
    src/tree.c:200:43: error: macro "debug_print_tree" passed 2 arguments, but takes just 1
      debug_print_tree("Appended sibling", node);
                                               ^
    src/tree.c:200:2: error: ‘debug_print_tree’ undeclared (first use in this function)
      debug_print_tree("Appended sibling", node);
      ^
    src/tree.c: In function ‘mq_tree_remove_allocated’:
    src/tree.c:247:39: error: macro "debug_print_tree" passed 2 arguments, but takes just 1
      debug_print_tree("Removed node", node);
                                           ^
    src/tree.c:247:2: error: ‘debug_print_tree’ undeclared (first use in this function)
      debug_print_tree("Removed node", node);
      ^

1 files changed, 1 insertions, 1 deletions

diff --git a/src/tree.c b/src/tree.c
index c940fae..8d6fee5 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -96,7 +96,7 @@ debug_print_head(const gchar *head, MqTree *node)
 
 #else  /* MQ_TREE_DEBUG */
 
-#define debug_print_tree(node)
+#define debug_print_tree(msg, node)
 #define debug_print_node(node)
 #define debug_print_head(head, node)