[__opendkim] FreeBSD: Fix service name inconsistency

This was going to be taken care of in __start_on_boot, but the solution to that
ended up not being generic enough; so this is what we get >,<.

While at it, add various variable value checks where it made sense.

type/__opendkim/files/opendkim.conf.sh

@@ -34,8 +34,8 @@ then
 fi
 
 # Key and Domain tables
-echo "KeyTable ${CFG_DIR}/KeyTable"
-echo "SigningTable ${CFG_DIR}/SigningTable"
+echo "KeyTable ${CFG_DIR:?}/KeyTable"
+echo "SigningTable ${CFG_DIR:?}/SigningTable"
 
 # Required socket to listen on
 printf "Socket %s\n" "${SOCKET:?}"

type/__opendkim/manifest

@@ -22,13 +22,17 @@ os=$(cat "${__global:?}/explorer/os")
 
 CFG_DIR="/etc/opendkim"
 service="opendkim"
+start_service="opendkim"
 case "$os" in
 'alpine')
 	:
 	;;
 'freebsd')
 	CFG_DIR="/usr/local/etc/mail"
+	# This is for 'service X start'
 	service="milter-opendkim"
+	# This is for __start_on_boot (it's inconsistent)
+	start_service="milteropendkim"
 	;;
 *)
 	printf "__opendkim does not yet support %s.\n" "$os" >&2
@@ -75,7 +79,7 @@ fi
 
 # Generate and deploy configuration file.
 source_file="${__object:?}/files/opendkim.conf"
-target_file="${CFG_DIR}/opendkim.conf"
+target_file="${CFG_DIR:?}/opendkim.conf"
 
 mkdir -p "${__object:?}/files"
 
@@ -90,11 +94,11 @@ fi
 require="__package/opendkim" __file "$target_file" \
 	--source "$source_file" --mode 0644
 
-require="__package/opendkim" __start_on_boot "${service}"
+require="__package/opendkim" __start_on_boot "${start_service:?}"
 
 # Ensure Key and Signing tables exist and have proper permissions
-key_table="${CFG_DIR}/KeyTable"
-signing_table="${CFG_DIR}/SigningTable"
+key_table="${CFG_DIR:?}/KeyTable"
+signing_table="${CFG_DIR:?}/SigningTable"
 
 require="__package/opendkim" \
 	__file "${key_table}" \
@@ -105,7 +109,7 @@ require="__package/opendkim" \
 	--mode 444
 
 require="__file${target_file} __file${key_table}
-		__file${signing_table} __start_on_boot/${service}" \
+		__file${signing_table} __start_on_boot/${start_service}" \
 	__check_messages opendkim \
 		--pattern "^__file${target_file}" \
 		--execute "service ${service} restart"