Fix ClassCastException in CharacterSets.getChar() when prompted for
password when using SSH PreConnectHandler.

Stack is :
java.lang.ClassCastException: java.lang.Character cannot be cast to
java.lang.Integer
    at com.jediterm.terminal.emulator.charset.CharacterSets.getChar
(CharacterSets.java:159)
    at com.jediterm.terminal.emulator.charset.GraphicSetState.map
(GraphicSetState.java:79)
    at com.jediterm.terminal.display.JediTerminal.decode
(JediTerminal.java:141)
    at com.jediterm.terminal.display.JediTerminal.writeString
(JediTerminal.java:135)
    at com.jediterm.terminal.display.JediTerminal.writeUnwrappedString
(JediTerminal.java:168)
    at com.jediterm.terminal.ui.PreConnectHandler.questionVisible
(PreConnectHandler.java:31)
Merge pull request #18 from Plonk42/char_cast_bug

Fix ClassCastException in when prompted for password