Apple II DeskTop allows the user to attempt to replace a file or folder with itself in the File > Copy a File... dialog box

[c0mmander8]

Describe the bug
Apple II DeskTop allows the user to attempt to replace a file or folder with itself in the File > Copy a File... dialog box.

To Reproduce
Steps to reproduce the behavior:

1. Start Apple II DeskTop.
2. Click on the File menu and go to File > Copy a File....
3. Select a file, not a folder, in the root directory of a volume.
4. Click OK.
5. Click OK again without doing anything else.
6. The "Copy..." dialog box appears stating, "That file already exists. Do you want to write over it?".
7. Click Yes.
8. An error message dialog box appears stating, "System Error".
9. Click OK.
10. The copy is cancelled.

Expected behavior
The "That name already exists. Please use another name." error message alert dialog box should appear instead when the user attempts to replace a file or folder with itself in the File > Copy a File... dialog box. The File > Copy a File... dialog box should not be dismissed so that the user can either choose another filename for the file or folder, choose another location to copy the file or folder or choose a different file or folder to copy.

Screenshots
I am sorry. I have no screenshots to help explain my problem.

System Details (please complete the following information):

• System [e.g. Apple IIe Enhanced, Apple IIc, Apple IIgs] Apple IIGS (ROM 01)
• Emulator? [e.g. real hardware, or emulator name] GSplus 0.14 (the latest version of the program)
• ProDOS version ProDOS 2.4.2 (the latest version)
• DeskTop version (from About > Apple II DeskTop...) Apple II DeskTop 1.2 Alpha 40 (the latest version of the program)
• Other [e.g. mouse, memory expansions, disk types, etc]

Additional context
As referenced in issue #536, this would be a good time to implement issue #449 and issue #450, if you decide to reconsider your position on those issues. "System error." really looks better than "System Error" and "I/O error." really looks better than "I/O Error.".