Switch ordering of coalesced values

[abhay]

The COALESCE function returns the first non-NULL argument so we were losing the new value for the old one if it wasn't NULL which is the opposite of what we wanted.

CC: @madninja

[abhay]

Showing that ordering matters for the PR history

etl=> select block, coalesce(block, 441087) from gateway_status where address = '11VVxHxDN8Soxo7ATugLJBfKDXdQdAhGCeRkbXBKGM4evPgvTp5';
 block  | coalesce 
--------+----------
 434982 |   434982
(1 row)

etl=> select block, coalesce(441087, block) from gateway_status where address = '11VVxHxDN8Soxo7ATugLJBfKDXdQdAhGCeRkbXBKGM4evPgvTp5';
 block  | coalesce 
--------+----------
 434982 |   441087
(1 row)

etl=> select block, coalesce(NULL, block) from gateway_status where address = '11VVxHxDN8Soxo7ATugLJBfKDXdQdAhGCeRkbXBKGM4evPgvTp5';
 block  | coalesce 
--------+----------
 434982 |   434982
(1 row)

etl=> select block, coalesce(441087, NULL) from gateway_status where address = '11VVxHxDN8Soxo7ATugLJBfKDXdQdAhGCeRkbXBKGM4evPgvTp5';
 block  | coalesce 
--------+----------
 434982 |   441087
(1 row)

etl=> select block, coalesce(NULL, NULL) from gateway_status where address = '11VVxHxDN8Soxo7ATugLJBfKDXdQdAhGCeRkbXBKGM4evPgvTp5';
 block  | coalesce 
--------+----------
 434982 | 
(1 row)