custom module deadlock import fix

[caronc]

Description:

Related issue (if applicable): #1075

Deadlock issue resolved that was created in #1071

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• 100% test coverage

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in as follows:
python3 -m venv apprise

# Change into our new directory
cd apprise

# Activate our virtual environment
source bin/activate

# Install the branch
pip install git+https://github.com/caronc/apprise.git@1075-custom-module-deadlock-fix

cat << _EOF > test.py
from apprise.decorators import notify

@notify(on="test")
def my_wrapper(body, title, *args, **kwargs):
  print(f"{title}: {body}")
_EOF

# Test out the changes with the following command:
apprise -t "Test Title" -b "Test Message" \
  -P ./test.py  test://

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.27%. Comparing base (b4798e3) to head (251fa4c).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1077      +/-   ##
==========================================
- Coverage   99.27%   99.27%   -0.01%     
==========================================
  Files         136      136              
  Lines       17753    17752       -1     
  Branches     3623     3622       -1     
==========================================
- Hits        17625    17624       -1     
  Misses        119      119              
  Partials        9        9              

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