Apart from calling write_stderr() on failure, the handler depends on no
PostgreSQL facilities.  We have experienced crashes before reaching the
former call site.  Given such an early crash, this change cannot hurt
and may produce a helpful dump.  Absent an early crash, this change has
no effect.  Back-patch to 9.3 (all supported versions).

Takayuki Tsunakawa

Discussion: https://postgr.es/m/0A3221C70F24FB45833433255569204D1F80CD13@G01JPEXMBYT05