rgw_sal_motr: [CORTX-33766] Fix for CopyObject API for zero byte object.

Problem:
CopyObject operation fails for zero byte object with 'NoSuchKey' error.

Solution:
Read/write to Motr only if object size is greater than zero.

Signed-off-by: Shriya Deshmukh <[email protected]>

Author: shriya-deshmukh

src/rgw/rgw_sal_motr.cc

@@ -2420,11 +2420,14 @@ int MotrObject::copy_object_same_zone(RGWObjectCtx& obj_ctx,
     return rc;
   }
 
-  // read::iterate -> handle_data() -> write::process
-  rc = read_op->iterate(dpp, cur_ofs, cur_end, filter, y);
-  if (rc < 0){
-    ldpp_dout(dpp, 20) << "ERROR: read op iterate failed rc=" << rc << dendl;
-    return rc;
+  // read from/write to motr, if source object is non empty object.
+  if (obj_size > 0){
+    // read::iterate -> handle_data() -> write::process
+    rc = read_op->iterate(dpp, cur_ofs, cur_end, filter, y);
+    if (rc < 0){
+      ldpp_dout(dpp, 20) << "ERROR: read op iterate failed rc=" << rc << dendl;
+      return rc;
+    }
   }
 
   real_time time = ceph::real_clock::now();