exists is faster than checking value; typo

[bieron]

I considered writing tests but all I could think of was in reality testing code underneath, like Net::SFTP::Foreign for &stfp. So I settled for little things instead... really tried to find something more substantial :)

[salva]

Patch applied with changes.

Using exists in that code patch just to gain a few nanoseconds doesn't make sense, I prefer to have simpler code.