Fast session resumption segfault

[Alan DeKok]

Phil Mayers wrote:
> Oops; I applied the patch in c145c7dabbd48 to my 2.1.12 servers, and
> last night we had a segfault after running fine for several hours. I
> restarted under GDB and caught a backtrace:
> 
> #0  paircopyvp (vp=0x101010101010101) at valuepair.c:327

  That's not a real pointer...

  I've pushed a "fix".  It sets the cached VP pointer to NULL when it
gets deleted.  That may help...

  Otherwise, it's an OpenSSL bug for it to return an invalid pointer.

  Alan DeKok.