Call shutdown() in connect() on exception

to clean up the state build up by connect().

Related to SMACK-855 there is the possiblitiy of a stray (writer)
thread if, for example, tlsHandled.checkifSuccessOrWaitorThrow() in
XMPPTCPConnection.connectInternal() throws. This commit should prevent
that.

smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java

@@ -478,9 +478,7 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
         shutdown(false);
     }
 
-    /**
-     * Performs an unclean disconnect and shutdown of the connection. Does not send a closing stream stanza.
-     */
+    @Override
     public synchronized void instantShutdown() {
         shutdown(true);
     }