Update spec with a couple more cases

Also fix a bad copypasta.

spec/lib/rex/proto/pjl/client_spec.rb

@@ -128,7 +128,9 @@ describe Rex::Proto::PJL::Client do
 
     context "#fsdownload" do
       it "should raise an exception due to an invalid path" do
-        expect { cli.fsdownload("BAD") }.to raise_error(ArgumentError)
+        expect { cli.fsdownload("/etc/passwd", "BAD") }.to raise_error(ArgumentError)
+        expect { cli.fsdownload("/etc/passwdd", "1:") }.to raise_error(Errno::ENOENT)
+        expect { cli.fsdownload("/etc/shadow", "1:") }.to raise_error(Errno::EACCES)
       end
 
       it "should upload a file" do