Basename cannot contain .. prevents valid filenames from being sent, no sender-side warning

[zulc22]

securing channel...basename cannot contain '..': 'Dragon Quest III - Soshite Densetsu e... (Japan).zip'

This error message prevented a transfer from occurring that took like five minutes to hash all the files, I understand it's probably a security thing to prevent files from going into unintended directories, but shouldn't the search string be '../', or '..\'? The sender side also had no warning for this and just spat EOF after the receiver connected. I think that both of these concerns could be addressed by checking the filenames with the same check on the server side, and that the substring should be changed.

[schollz]

Feel free to make a pr!