Fix in RDKitDescriptors

[arunppsg]

Description

Fix #3483

Update program logic in setting labels only attribute in RDKitDescriptors. Earlier, it was features[features != 0] = 1. Here, features is a list and features != 0 computed whether features is 0 or not. This is
incorrect as we have to compare elements of features with 0 and not the list itself. The update uses
np.putmask to mask elements and replace others with 1.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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• Documentations (modification for documents)

Checklist

• My code follows the style guidelines of this
  project
  • Run yapf -i <modified file> and check no errors (yapf version must be 0.32.0)
  • Run mypy -p deepchem and check no errors
  • Run flake8 <modified file> --count and check no errors
  • Run python -m doctest <modified file> and check no errors
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

[rbharath]

LGTM