Check SQLite3 WAL size before initialization

[PimSanders]

When trying to initialize the SQLite3 WAL class an EOFError is thrown if the WAL file exists, but is empty. This PR fixes the issue by verifying that the size of the WAL file is non zero.

Required for fox-it/dissect.target#1454.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.02%. Comparing base (33bc02a) to head (28a3faa).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
+ Coverage   81.91%   82.02%   +0.10%     
==========================================
  Files          31       31              
  Lines        2334     2348      +14     
==========================================
+ Hits         1912     1926      +14     
  Misses        422      422              

Flag	Coverage Δ
unittests	82.02% <100.00%> (+0.10%)	⬆️

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[Schamper]

Looks good but I thought of a small other improvement:

Can you add a close method that closes any file handle we opened ourselves, in case we passed a Path? Don't close it if we received a file-like object.

And add a __enter__ (that just returns self) and __exit__ (that calls close()). Then we can use context managers in dissect.target.