Improve SQLite table exist checks

[JSCU-CNI]

This PR makes sure the wpndatabase plugin checks if the NotificationHandler table exists before attempting to read from it.

[codecov]

Codecov Report

Attention: Patch coverage is 25.45455% with 41 lines in your changes missing coverage. Please review.

Project coverage is 77.89%. Comparing base (5c9eedf) to head (0e6d5da).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/target/plugins/os/unix/esxi/_os.py	0.00%	28 Missing ⚠️
dissect/target/loaders/itunes.py	0.00%	3 Missing ⚠️
dissect/target/plugins/apps/browser/iexplore.py	40.00%	3 Missing ⚠️
...ssect/target/plugins/os/windows/activitiescache.py	0.00%	3 Missing ⚠️
dissect/target/plugins/os/windows/catroot.py	50.00%	3 Missing ⚠️
dissect/target/plugins/os/windows/notifications.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
- Coverage   77.91%   77.89%   -0.02%     
==========================================
  Files         324      324              
  Lines       27869    27879      +10     
==========================================
+ Hits        21714    21717       +3     
- Misses       6155     6162       +7     

Flag	Coverage Δ
unittests	77.89% <25.45%> (-0.02%)	⬇️

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