Fix: only chmod when there are files

[casperklein]

Description

Fix for:

[   INF   ]  Welcome to docker-mailserver 11.3.1
[   INF   ]  Checking configuration
[   INF   ]  Configuring mail server
chmod: cannot access '/usr/lib/dovecot/sieve-filter/*': No such file or directory
chmod: cannot access '/usr/lib/dovecot/sieve-pipe/*': No such file or directory  

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[polarathene]

Curious why we set chmod 755 and not chmod -R 755 since this is only matching directories? If we're fixing permissions there, I assume that might be relevant to the contents too 🤔

[georglauterbach]

The fix appears to be correct to me, since we do not want to adjust the contents of the dirs, only the dirs, so the -R is not needed and not desired as well (as contents and dirs need different dirs).

If you were using -R, you'd be adjusting the contents as well, even though the find only matches dirs.