Add TODO item for putty and CVE-2019-989{4,5,7,8} issues

The issue might be fixed already with the targetted upload to unstable
as 0.70-6 with the following changelog entry:

	 putty (0.70-6) unstable; urgency=high
	 .
	   * Apply security patch series from upstream:
	     - New facility for removing pending toplevel callbacks.
	     - Fix one-byte buffer overrun in random_add_noise().
	     - uxnet: clean up callbacks when closing a NetSocket.
	     - sk_tcp_close: fix memory leak of output bufchain.
	     - Fix handling of bad RSA key with n=p=q=0.
	     - Sanity-check the 'Public-Lines' field in ppk files.
	     - Introduce an enum of the uxsel / select_result flags.
	     - Switch to using poll(2) in place of select(2).
	     - RSA kex: enforce the minimum key length.
	     - Fix crash on ESC#6 + combining chars + GTK + odd-width terminal.
	     - Limit the number of combining chars per terminal cell.
	     - minibidi: fix read past end of line in rule W5.

but CVE commit association needs to be determined.