loglist: error when every log list source fails

FetchAll swallowed per-source errors and always returned nil, so all
three upstreams failing was indistinguishable from an empty log list
and the hourly sync silently tailed nothing. Total failure now
returns an error; partial failure logs a warning.

internal/loglist/loglist.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"time"
 )
@@ -89,11 +90,13 @@ func FetchAll(client *http.Client) ([]Log, error) {
 	urls := []string{ChromeList, ChromeAllList, AppleList}
 	seen := make(map[string]*Log)
 	var order []string
+	var fetched int
 	for _, u := range urls {
 		list, err := fetchOne(client, u)
 		if err != nil {
 			continue
 		}
+		fetched++
 		for i := range list.Operators {
 			for j := range list.Operators[i].Logs {
 				lg := &list.Operators[i].Logs[j]
@@ -121,6 +124,12 @@ func FetchAll(client *http.Client) ([]Log, error) {
 	for _, id := range order {
 		out = append(out, *seen[id])
 	}
+	if fetched == 0 {
+		return nil, fmt.Errorf("all %d log list sources failed", len(urls))
+	}
+	if fetched < len(urls) {
+		log.Printf("loglist: %d of %d sources failed", len(urls)-fetched, len(urls))
+	}
 	return out, nil
 }