fix: do not try to slice in chunk larger than the File itself

[skjnldsv]

Context

If you try to upload a large file (like 2GB) with chunk upload disabled, the browser will misbehave

Resolution

We stop slicing the entire file and we just return its blob directly

Fix nextcloud/server#42704

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1d31c8b) 91.25% compared to head (3e40a97) 16.85%.
Report is 3 commits behind head on master.

❗ Current head 3e40a97 differs from pull request most recent head 5f3b0d4. Consider uploading reports for the commit 5f3b0d4 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1057       +/-   ##
===========================================
- Coverage   91.25%   16.85%   -74.40%     
===========================================
  Files           3        9        +6     
  Lines          80      445      +365     
  Branches       16       77       +61     
===========================================
+ Hits           73       75        +2     
- Misses          4      367      +363     
  Partials        3        3               

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