Memory leak: file is not closed if TransferOpen() fails

[marshallbrekka]

https://github.com/fclairamb/ftpserver/blob/d06e1a0d4a20bf8a311961952b15c550a1acbfd9/server/handle_files.go#L22-L35

The file opened on line 22 is never closed if the TransferOpen() call fails.
You could of course call file.Close() within that else block, my only concern is that still results in an empty file being created.

Another option is to call TransferOpen() first, and then attempt to open the file.

I can submit a PR once a solution is agreed upon.

[fclairamb]

I just checked, in that scenario, proftpd creates an empty file.

So I think it's quite acceptable to behave the same way.

[fclairamb]

PR #71 fixes this.