Move deleteDownloadTask to be after file opened

[BPerlakiH]

Fixes: #992

The main issue was that the UI listened to the download task, that is in progress, if it is not existing the UI will return to the initial state (the file is downloadable). Once the downloaded file is moved and opened (which is async now), the "Open Main Page" will be displayed on the UI.

Solution:
Move the delete download task after the file has been opened, this will keep the UI in the progress state.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 38.00%. Comparing base (2ff9049) to head (739af80).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
Model/DownloadService.swift	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #998      +/-   ##
==========================================
- Coverage   39.98%   38.00%   -1.99%     
==========================================
  Files         114      114              
  Lines        6470     6471       +1     
==========================================
- Hits         2587     2459     -128     
- Misses       3883     4012     +129     

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