give a clear message if model.get_ntypes()<data.get_ntypes()

[njzjz]

Fix #1015.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.01%. Comparing base (d42ca99) to head (8f57fb3).

Files with missing lines	Patch %	Lines
deepmd/train/trainer.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #1016      +/-   ##
==========================================
- Coverage   75.02%   75.01%   -0.02%     
==========================================
  Files          86       86              
  Lines        6923     6924       +1     
==========================================
  Hits         5194     5194              
- Misses       1729     1730       +1     

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