salt-key fails but exits with 0 (redux)

Description of Issue

Identical to #18562 and #42468. According to those reports, this is a duplicate of #18510 and should have been corrected in Flourine. That does not appear to be the case.

Setup

curl -o bootstrap-salt.sh -L https://bootstrap.saltstack.com
sudo sh bootstrap-salt.sh -M
sudo salt-key -a some_nonexistent_key -y
echo $?

Steps to Reproduce Issue

INCORRECT: The above echoes "0"
CORRECT: The above echoes something other than "0"

Versions Report

           Salt: 2019.2.0
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: 2.0.3
      gitpython: 2.1.8
          ioflo: Not Installed
         Jinja2: 2.10
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Jan 14 2019, 11:02:34)
   python-gnupg: 0.4.1
         PyYAML: 3.12
          PyZMQ: 16.0.2
           RAET: Not Installed
          smmap: 2.0.3
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.5
 
System Versions:
           dist: Ubuntu 18.04 bionic
         locale: UTF-8
        machine: x86_64
        release: 4.15.0-55-generic
         system: Linux
        version: Ubuntu 18.04 bionic

Start by reproducing the reported command sequence with salt-key and confirm the exit status when approving a nonexistent key. Trace the salt-key command's failure handling and verify that the command returns a nonzero status while preserving successful behavior for valid keys.