Skip the op msg when the entity has been drop

[SimFG]

issue: #36

[codecov-commenter]

Codecov Report

Attention: 519 lines in your changes are missing coverage. Please review.

Comparison is base (5e2ce2e) 81.59% compared to head (44a2ce9) 74.64%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   81.59%   74.64%   -6.95%     
==========================================
  Files          38       39       +1     
  Lines        4096     4852     +756     
==========================================
+ Hits         3342     3622     +280     
- Misses        626     1043     +417     
- Partials      128      187      +59     

Files	Coverage Δ
core/reader/channel_reader.go	96.73% <100.00%> (ø)
core/reader/collection_reader.go	81.48% <100.00%> (+1.97%)	⬆️
server/metrics/metrics.go	76.92% <100.00%> (+1.92%)	⬆️
server/writer_callback.go	100.00% <100.00%> (ø)
core/api/data_handler.go	84.21% <0.00%> (-4.68%)	⬇️
core/api/meta_op.go	87.50% <0.00%> (-12.50%)	⬇️
server/server.go	78.57% <0.00%> (-1.92%)	⬇️
core/util/atomic.go	91.30% <60.00%> (-5.31%)	⬇️
core/util/retry_option.go	59.09% <50.00%> (-40.91%)	⬇️
core/writer/milvus_handler.go	92.53% <75.00%> (-5.11%)	⬇️
... and 6 more