www/lighttpd: fix regression on service restart

Problem:

Performing sanity check on lighttpd configuration:
lighttpd not running? (check /var/run/lighttpd.pid).
Starting lighttpd.
2021-10-12 23:02:07: (network.c.419) can't bind to socket: 0.0.0.0:80: Address already in use
/usr/local/etc/rc.d/lighttpd: WARNING: failed to start lighttpd

Workaround:

Performing sanity check on lighttpd configuration:
lighttpd not running? (check /var/run/lighttpd.pid).
Starting lighttpd.

Diagnostics:

When "lighttpd_checkconfig" runs,
the content of the pid file is removed.

PR: 259114
Submitted by: dinoex