fix(FilePicker): Set default of path to undefined to allow using the saved path

[susnux]

• Part of Folder Smart Picker broken nextcloud/server#40866

Bring back the "saved path" or "last path" feature.

The property should default to undefined to the check in the computed property (currentPath) can use the last saved path as a fallback.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9445962) 30.61% compared to head (5a800bb) 30.61%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1137   +/-   ##
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  Coverage   30.61%   30.61%           
=======================================
  Files          16       16           
  Lines        1225     1225           
  Branches       60       60           
=======================================
  Hits          375      375           
  Misses        792      792           
  Partials       58       58           

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