Fix: Handle invalid form hashes correctly

[Chartman123]

This fixes #2651 by correctly catching the NotFoundException in the backend and passing a corresponding value to the inital state of the app.

The formId is then checked against the defined value and routeAllowed returns false which then shows the correct error message that the form could not be found.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 43.31%. Comparing base (f48d88b) to head (d4ef335).
Report is 16 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2655      +/-   ##
============================================
- Coverage     43.34%   43.31%   -0.04%     
- Complexity      887      888       +1     
============================================
  Files            78       78              
  Lines          3368     3371       +3     
============================================
  Hits           1460     1460              
- Misses         1908     1911       +3     

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[Chartman123]

/backport to stable4