MDEV-11435 - fix integer divided by zero exception when calculating buffer pool size
MDEV-11435 - fix integer divided by zero exception when calculating
buffer pool size

The reason for the exception is previous overflow in multiplication of
two 32bit integers (product was 0 rather than expected 8GB, due
to truncation)

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2