Fix authorization checks in attachment upload

[RadovanTomik]

Negotiator pull request:

Description:

Fix authorization checks in attachment upload.

Checklist:

Make sure you tick all the boxes bellow if they are true or do not apply:

• I have performed a self review of my code
• My code follows Google Java Code style
• I have made my code as simple as possible
• I have added unit tests and the code coverage has not decreased
• I have updated the documentation in all relevant places

[codecov]

Codecov Report

Attention: Patch coverage is 79.16667% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 76.80%. Comparing base (ce1903a) to head (7e174a1).

Files	Patch %	Lines
...i_eric/negotiator/service/DBAttachmentService.java	85.00%	1 Missing and 2 partials ⚠️
...iator/api/controller/v3/NegotiationController.java	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #267      +/-   ##
============================================
- Coverage     78.24%   76.80%   -1.45%     
+ Complexity      890      869      -21     
============================================
  Files           122      122              
  Lines          2708     2716       +8     
  Branches        154      157       +3     
============================================
- Hits           2119     2086      -33     
- Misses          490      524      +34     
- Partials         99      106       +7     

Flag	Coverage Δ
unit	76.80% <79.16%> (-1.45%)	⬇️

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