fix possible tooltip exception

if it is set to ""

java.lang.IllegalArgumentException: Width and height must be >= 0
Width and height must be >= 0
javax.swing.plaf.basic.BasicHTML.getHTMLBaseline(Unknown Source)
javax.swing.plaf.metal.MetalToolTipUI.paint(Unknown Source)
fix empty tooltips

fixes also:
java.lang.IllegalArgumentException: Width and height must be >= 0
Width and height must be >= 0
javax.swing.plaf.basic.BasicHTML.getHTMLBaseline(Unknown Source)
javax.swing.plaf.metal.MetalToolTipUI.paint(Unknown Source)
fix cancelling of keyboard-interactive authentication

fixes:
java.lang.NullPointerException
null
ch.ethz.ssh2.util.StringEncoder.GetBytes(StringEncoder.java:17)
ch.ethz.ssh2.packets.TypesWriter.writeString(TypesWriter.java:136)
ch.ethz.ssh2.packets.PacketUserauthInfoResponse.getPayload(PacketUserauthInfoResponse.java:29)
ch.ethz.ssh2.auth.AuthenticationManager.authenticateInteractive(AuthenticationManager.java:381)
fix stonith devices not being configurable