krb5int_derive_key results in cache with uninitialized values

krb5int_derive_key results in cache with uninitialized values

krb5int_derive_key creates a temporary keyblock to add to the derived cache.
krb5_k_free_key will iterate over the derived keys and for ones with cache will
lookup the enctype for the key_cleanup handler.

Unfortunatly, there isn't a keyblock init function that does not allocate the
keyblock - as I suspect this problem will appear in other places.

The valgrind log of this problem is:

==7281== Conditional jump or move depends on uninitialised value(s)
==7281==    at 0x40E9AE8: find_enctype (etypes.h:81)
==7281==    by 0x40E9C96: krb5_k_free_key (key.c:91)
==7281==    by 0x40E9C52: krb5_k_free_key (key.c:86)
==7281==    by 0x40EBB00: krb5_c_prf (prf.c:87)
==7281==    by 0x40E7B1B: prf_plus (cf2.c:77)
==7281==    by 0x40E7CE6: krb5_c_fx_cf2_simple (cf2.c:125)
==7281==    by 0x804899C: main (t_cf2.c:70)
==7281==

with memory leaks.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23608 dc483132-0cff-0310-8789-dd5450dbe970