ITS#9338 alternate fix

Don't resume pending ops unless there are no other threads
waiting to write
3 jobs for its9338b in 30 minutes and 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #1930
build-gnutls-mit

00:26:56

passed #1928
build-no-threads-no-slapd

00:03:28

passed #1929
build-openssl-heimdal

00:28:31