gc.c: fix compile error

* gc.c (gc_prepare_free_objects): fix compile error.  there should be
  free objects when new slot is added.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39902 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

gc.c

@@ -2048,7 +2048,7 @@ gc_prepare_free_objects(rb_objspace_t *objspace)
 
     if (!GC_ENABLE_LAZY_SWEEP || objspace->flags.dont_lazy_sweep) {
 	if (heaps_increment(objspace)) {
-	    return;
+	    return TRUE;
 	}
 	else {
 	    return garbage_collect(objspace);