[m-rev.] diff: Fix crash in mdb help command.

[Peter Wang]

trace/mercury_trace_help.c:
    Fix swapped arguments in call to ML_HELP_print_top_level_help_nodes.
    This bug was introduced in commit a06ae2c6ef196972d1abfef586041bee20561401

diff --git a/trace/mercury_trace_help.c b/trace/mercury_trace_help.c
index 984c97304..9297c97bc 100644
--- a/trace/mercury_trace_help.c
+++ b/trace/mercury_trace_help.c
@@ -119,8 +119,8 @@ MR_trace_help(void)
     MR_c_file_to_mercury_file(MR_mdb_out, &mdb_out);
 
     MR_TRACE_CALL_MERCURY(
-        ML_HELP_print_top_level_help_nodes(MR_trace_help_system,
-            MR_wrap_output_stream(&mdb_out));
+        ML_HELP_print_top_level_help_nodes(MR_wrap_output_stream(&mdb_out),
+            MR_trace_help_system);
     );
 }
 
-- 
2.28.0