Update ssh key FileChooser filter

[mbien]

key FileChooser (e.g terminal remote connection) will now also show openssh keys which have a longer key header

found this issue while testing #8848 and noticed that the file chooser didn't list my keys (both RSA and EC, created using OpenSSH)

[matthiasblaesing]

Only eyeballed this, but looks ok to me.

Maybe it would have been more readable, to just raise the buffer to 40 bytes, switch to try-with-resource and switch to DOTALL matching.

[mbien]

Maybe it would have been more readable, to just raise the buffer to 40 bytes, switch to try-with-resource and switch to DOTALL matching.

that was my original impl. But I wanted to avoid reading into the key with string operations in UI code. I don't want to see parts of the key in Strings or heap dumps unless there is no other way of doing that. I hope its still simple enough.