Currently systemd does not support seperate ExecReloadPre command to
check if safe reload is possible.[0] It should be possible to emulate
similar behavior with multible ExecPreload lines but due to systemd
issue #11238 it is not currently possible.[1]

Current workaround is to tell systemd to ignore ExecReload command exit
code and put a oneliner shell script in there that checks if its safe to
reload nginx config files. Unfortunaly this does not give any feedback
on the running terminal if reload failed or not.

Fix for #11238 should land in systemd v243 some time in the future

[0] https://github.com/systemd/systemd/issues/2175
[1] https://github.com/systemd/systemd/issues/11238