#9 Fix crash on corrupt known_hosts file

[Robin Neatherway]

The exception is raised in the case where a server host key is bad. In
my case the system administrator had accidentally included the key
type twice:

server.company.com,10.0.0.1 ssh-rsa ssh-rsa <key>

And ssh-rsa was treated as a key. This fails because it is not valid
Base64. My proposed patch treats this line as an invalid line and
continues, like JSch does in other cases.

$ diff -u ./src/main/java/com/jcraft/jsch/KnownHosts.java ./src/main/java/com/jcraft/jsch/KnownHosts2.java
--- ./src/main/java/com/jcraft/jsch/KnownHosts.java 2017-03-28 09:55:32.131080050 +0100
+++ ./src/main/java/com/jcraft/jsch/KnownHosts2.java    2017-03-28 09:57:26.322732339 +0100
@@ -215,12 +215,14 @@
    //System.err.println(host);
    //System.err.println("|"+key+"|");

-   HostKey hk = null;
-        hk = new HashedHostKey(marker, host, type, 
-                               Util.fromBase64(Util.str2byte(key), 0, 
-                                               key.length()), comment);
-   pool.addElement(hk);
-      }
+        try {
+          pool.addElement(new HashedHostKey(marker, host, type, 
+                                            Util.fromBase64(Util.str2byte(key), 0, 
+                                                            key.length()), comment));
+        } catch (JSchException e) {
+          addInvalidLine(Util.byte2str(buf, 0, bufl));
+        }
+
       if(error){
    throw new JSchException("KnownHosts: invalid format");
       }