patch 9.2.0353: Missing out-of-memory check in register.c

patch 9.2.0353: Missing out-of-memory check in register.c

Problem:  Missing out-of-memory check in register.c
Solution: Check for memory allocation failure and return NULL
          (John Marriott).

closes: #19949

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>