[rcore] Fix FileMove from delete file if FileCopy did not work

[Lucrecious]

Hello!

I was making a file browser in my favourite graphics library (raylib), and needed file move functionality.

The issue was that despite the function running and leaving no errors, it was deleting my file instead of moving it!

I noticed that FileCopy seems to return 1 if SaveFileData returns true and 0 otherwise, but some other FileX functions return 0 if the operation succeeds - so I wasn't sure what to fix!

1. Is FileCopy supposed return 0 if it succeeds or
2. is the intended functionality for it to return 1 for success but the bug is in FileMove?

Anyway, I went with the solution that preserves backwards compatibility and assumes that FileCopy cannot change what it returns until... 7.0?

[raysan5]

@Lucrecious Wow! Good catch! It will be updated for new release 6.1 or 6.2