This fixes a scan-build false-positive:

rbt_test.c:914:8: warning: Assigned value is garbage or undefined
                node %= *names_count;
                     ^  ~~~~~~~~~~~~
1 warning generated.

The remove_nodes() function is always called with correct arguments
(num_names is in <1;*names_count> range), so the modulo by zero cannot
happen, but nevertheless scan-build detects this and it's easy to fix.