Fix error in determin apache2 systemd service file. runs into an error, if apache2 was installed from debian package system.

install_postfixadmin.sh

@@ -147,11 +147,11 @@ if $systemd_supported ; then
 	# - Is Service exclusive controlled by systemd
 	# -
 	if systemctl -t service list-unit-files \
-			| grep -e "^apache" \
+			| grep -e "^apache2.service" \
 			| grep -q -E "(enabled|disabled)" 2> /devnull ; then
 
 		APACHE_SERVICE_FILE=$(systemctl -t service list-unit-files \
-										| grep -e "^apache" \
+										| grep -e "^apache2.service" \
 										| awk '{print$1}')
 
 	fi