[BUG] `env_order` does not work as advertised; omitted envs can't be included

Description

The docs at https://docs.saltstack.com/en/latest/ref/configuration/master.html#env-order say (emphasis mine):

When top_file_merging_strategy is set to merge, and no environment is specified for a highstate, this config option allows for the order in which top files are evaluated to be explicitly defined.

But env_order is clearly being checked for a non-highstate state, and when an environment is explicitly specified.

Setup

Relevant master configuration excerpt:

file_roots:
  base:
    - /srv/salt
  dev:
    - /srv/salt/dev
env_order:
  - base

/srv/salt/dev/foo.sls:

include:
  - bar

/srv/salt/dev/bar.sls:

bar:
  test.succeed_without_changes: []

Steps to Reproduce the behavior

# salt-call state.apply foo saltenv=dev
[ERROR   ] Nonexistent saltenv 'dev' found in include of 'bar' within SLS 'dev:foo'
local:
    Data failed to compile:
----------
    No matching salt environment for environment 'dev' found
----------
    Nonexistent saltenv 'dev' found in include of 'bar' within SLS 'dev:foo'

Expected behavior

State should run. Both files are in the dev environment. If I add dev to the env_order, it works.

Versions Report

Salt Version:
           Salt: 3001
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.11.1
        libgit2: Not Installed
       M2Crypto: 0.35.2
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: Not Installed
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Apr  2 2020, 13:34:55)
   python-gnupg: Not Installed
         PyYAML: 3.13
          PyZMQ: 17.0.0
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.1.4
 
System Versions:
           dist: centos 7 Core
         locale: UTF-8
        machine: x86_64
        release: 5.4.0-42-generic
         system: Linux
        version: CentOS Linux 7 Core

Start by reproducing the failure with salt-call state.apply foo saltenv=dev and the shown env_order configuration. Trace how env_order, the explicit saltenv, and the include in dev:foo are handled, then verify that the state runs without adding dev to env_order and that the documented behavior is covered by a regression test.