add Buffer capacity check for type UInt64

[OlivierSalasc]

While working with openssh signed certificate of type ssh-rsa-cert-v01@openssh.com , i encountered the following exception :

java.lang.ArrayIndexOutOfBoundsException: 514
	at net.schmizz.sshj.common.Buffer.putUInt64Unchecked(Buffer.java:375)
	at net.schmizz.sshj.common.Buffer.putUInt64(Buffer.java:362)
	at net.schmizz.sshj.common.KeyType$CertUtils.writePubKeyContentsIntoBuffer(KeyType.java:340)
	at net.schmizz.sshj.common.KeyType$7.writePubKeyContentsIntoBuffer(KeyType.java:217)
	at net.schmizz.sshj.common.KeyType.putPubKeyIntoBuffer(KeyType.java:281)
	at net.schmizz.sshj.common.Buffer.putPublicKey(Buffer.java:477)
	at net.schmizz.sshj.userauth.method.KeyedAuthMethod.putPubKey(KeyedAuthMethod.java:51)
	at net.schmizz.sshj.userauth.method.AuthPublickey.buildReq(AuthPublickey.java:62)
	at net.schmizz.sshj.userauth.method.AuthPublickey.buildReq(AuthPublickey.java:81)
	at net.schmizz.sshj.userauth.method.AbstractAuthMethod.request(AbstractAuthMethod.java:68)
	at net.schmizz.sshj.userauth.UserAuthImpl.authenticate(UserAuthImpl.java:72)
	at net.schmizz.sshj.SSHClient.auth(SSHClient.java:225)
	at net.schmizz.sshj.SSHClient.authPublickey(SSHClient.java:346)
	at net.schmizz.sshj.SSHClient.authPublickey(SSHClient.java:365)

The cause of the issue is in the class net\schmizz\sshj\common\Buffer. When a 64-bit Uint is put in the buffer, the capacity of the buffer is neither checked or expanded (as it is done for the other types).

I fixed the issue and have added 2 units tests.

[hierynomus]

Thanks!