Choose a key file dialog ("all files") doesn't show files without an extension

[php4fan]

Steps to reproduce:

1. Go to Site Manager; edit or create a site
2. For "Protocol" choose SSH, and for "Logon type" choose "key file"
3. Click the "Browse..." button to browse for a key file
4. Browse to a directory that contains a private key file whose name does not contain any dot
5. In the file type dropdown selector at the bottom (by default "ppk files") select "All files"

Expected:
Since I have selected "All files", all files in the folder should be shown. Since there is a valid file as per step 4 (the fact that it has no extension should be irrelevant), that file should be shown, among others if any.

Observed:
The file is not listed.

The file is readable by my user. If I rename the file so it has ANY extension (e.g. "mykeyfile.wtf" instead of just "mykeyfile"), then the file is listed. And in this case I have tried selecting it and it works, confirming that it is a valid file (but this is not relevant because invalid files are also listed and you can choose them, then you'll get an error message when you try to use them).

So, when "all files" is selected, you show files with any extensions, but only if they do have an extension, that is, if the file name contains at least one dot. That makes no sense and it's something I've never seen anywhere else.