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-bosh/src/main/java/org/jivesoftware/smack/bosh/XMPPBOSHConnection.java

@@ -263,6 +263,11 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
             client = null;
         }
 
+        instantShutdown();
+    }
+
+    @Override
+    public void instantShutdown() {
         setWasAuthenticated();
         sessionID = null;
         done = true;