Fixed vmdk thin opening when parentFileNameHint was set to full path

[object1337]

Fixed VMDK thin opening when parentFileNameHint was set to full path

When attempting to mount a VMDK file that was created using thin
provisioning, it would fail with a file not found error on the parent VMDK
file, due to it attempting to find it in the same directory. However, the
parentFileNameHint was set to the full path of the parent VMDK file, but
ignored by dissect. This pull requests attempts to load the VMDK parent
file using the parentFileNameHint first, before continuing with the
existing loading method.

Fixes #77

[Schamper]

Maybe nice to swap it around, since I think for our purposes we generally have the first case scenario.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.04%. Comparing base (6f2d5ab) to head (4dc85d1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   78.64%   79.04%   +0.40%     
==========================================
  Files          26       26              
  Lines        2332     2334       +2     
==========================================
+ Hits         1834     1845      +11     
+ Misses        498      489       -9     

Flag	Coverage Δ
unittests	79.04% <100.00%> (+0.40%)	⬆️

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