[BUG] postfix.set_master breaks on line continuation

Description
When reading a postfix master.cf that has continued lines, set_master gets a line that doesn't match its expectations (ie 8 fields). Lines beginning with '#' are correctly ignored, but lines starting with whitespace should be ignored here as well. As per postfix docs at https://www.postfix.org/master.5.html:

SYNTAX
       The general format of the [master.cf](https://www.postfix.org/master.5.html) file is as follows:

       o      Empty  lines and whitespace-only lines are ignored, as are lines
              whose first non-whitespace character is a `#'.

       o      A logical line starts with  non-whitespace  text.  A  line  that
              starts with whitespace continues a logical line.

       o      Each  logical  line defines a single Postfix service.  Each ser-
              vice is identified by its name  and  type  as  described  below.
              When multiple lines specify the same service name and type, only
              the last one is remembered.  Otherwise, the order  of  [master.cf](https://www.postfix.org/master.5.html)
              service definitions does not matter.

       Each  logical  line  consists  of eight fields separated by whitespace.
       These are described below in the order as they appear in the  [master.cf](https://www.postfix.org/master.5.html)
       file.

       Where  applicable  a  field  of  "-" requests that the built-in default
       value be used. For boolean fields specify "y" or "n"  to  override  the
       default value.

Setup
Install postfix on ubuntu 20.04, try to use postfix.set_master. The file contains continuation lines which dont contain 8 "columns" eg:

...
smtp      unix  -       -       -       -       -       smtp
relay     unix  -       -       -       -       -       smtp
        -o syslog_name=postfix/$service_name
#       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq     unix  n       -       -       -       -       showq
...

Steps to Reproduce the behavior

salt-call postfix.set_master smtps inet n y n n 100 smtpd
# index out of range error

Expected behavior
postfix master config is updated

Versions Report
Salt Version:
Salt: 3004.1

Dependency Versions:
cffi: Not Installed
cherrypy: Not Installed
dateutil: 2.7.3
docker-py: Not Installed
gitdb: Not Installed
gitpython: Not Installed
Jinja2: 2.10.1
libgit2: Not Installed
M2Crypto: 0.31.0
Mako: Not Installed
msgpack: 0.6.2
msgpack-pure: Not Installed
mysql-python: Not Installed
pycparser: Not Installed
pycrypto: Not Installed
pycryptodome: 3.6.1
pygit2: Not Installed
Python: 3.8.10 (default, Mar 15 2022, 12:22:08)
python-gnupg: 0.4.5
PyYAML: 5.3.1
PyZMQ: 18.1.1
smmap: Not Installed
timelib: Not Installed
Tornado: 4.5.3
ZMQ: 4.3.2

System Versions:
dist: ubuntu 20.04 focal
locale: utf-8
machine: x86_64
release: 5.4.0-120-generic
system: Linux
version: Ubuntu 20.04 focal

Start by locating the postfix.set_master entry point and how it parses master.cf service lines. Reproduce the reported command with a configuration containing an indented continuation line, then verify that continuation lines no longer cause an index error and that the requested service is updated successfully.