Check for malloc failure in process_chpw_request

(cherry picked from commit 4356deefa2d2fe0bc7b52f3b62a387c7ec1eb369)

https://github.com/krb5/krb5/commit/f4bd63ff6492e3440a6e1e63fca8df880c060f65
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: f4bd63ff6492e3440a6e1e63fca8df880c060f65
Branch: krb5-1.12
 src/kadmin/server/schpw.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)