fix: Stronghold import failed with larger files

[obany]

Description of change

Stronghold files with only a small amount of data could not be imported as there was a limit on the file size.
Cleaned up the drop zone code.

Type of change

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• Bug fix (a non-breaking change which fixes an issue)

How the change has been tested

Tested on windows

Change checklist

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• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes