cls/rgw: make usage_iterate_range()'s "truncated" parameter trustworthy

Set it to false whenever we identify that we've reached the end of our
range, even if the underlying OSD op says it could have given us more
results. Then rely on that instead of weird iter-based logic to tell
our client that it doesn't need to do more work.

Fixes: https://tracker.ceph.com/issues/22963

Signed-off-by: Greg Farnum <gfarnum@redhat.com>
(cherry picked from commit 7ea8ca8)

src/cls/rgw/cls_rgw.cc

@@ -2958,12 +2958,18 @@ static int usage_iterate_range(cls_method_context_t hctx, uint64_t start, uint64
 
     if (!by_user && key.compare(end_key) >= 0) {
       CLS_LOG(20, "usage_iterate_range reached key=%s, done", key.c_str());
+      if (truncated) {
+	*truncated = false;
+      }
       key_iter = key;
       return 0;
     }
 
     if (by_user && key.compare(0, user_key.size(), user_key) != 0) {
       CLS_LOG(20, "usage_iterate_range reached key=%s, done", key.c_str());
+      if (truncated) {
+	*truncated = false;
+      }
       key_iter = key;
       return 0;
     }
@@ -3080,7 +3086,7 @@ int rgw_user_usage_log_trim(cls_method_context_t hctx, bufferlist *in, bufferlis
   if (ret < 0)
     return ret;
 
-  if (!more && iter.empty())
+  if (!more)
     return -ENODATA;
 
   return 0;