Avoid exiting when user misclick and cancel the load of a file

[tadeubas]

What is this PR for?

• Fixed bug when signing message with empty file
• Avoid exiting when user misclick and cancel the load of a file

What is the purpose of this pull request?

• Bug fix
• New feature
• Docs update
• Other

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.75%. Comparing base (fdee14e) to head (03678f9).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/krux/pages/file_manager.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #469      +/-   ##
===========================================
+ Coverage    94.70%   94.75%   +0.04%     
===========================================
  Files           70       70              
  Lines         7573     7581       +8     
===========================================
+ Hits          7172     7183      +11     
+ Misses         401      398       -3     

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[odudex]

Thank you!
It would be nice to add a test to cover new code and meet the patch requirements.

[odudex]

Thank you!