Fix panic when deleting last file in directory

[sahinfalcon]

Fixes #528.

Problem

If you try to delete the last file in a directory, the application would panic with an "index out of range [-1]" error. This occurred because the cursor position didn't reset properly after the deletion, leading to an invalid array
access in the file preview panel.

Solution

Added proper cursor position handling after file deletion:

• if the current directory is empty, the cursor becomes 0
• if the cursor is beyond last element, set it to last element position

[netlify]

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[yorukot]

Thank you so much!