WebAPI: Use specific number to represent non-existing values

Closes #15545.

src/webui/api/torrentscontroller.cpp

@@ -176,7 +176,7 @@ namespace
         const QJsonObject dht
         {
             {KEY_TRACKER_URL, "** [DHT] **"},
-            {KEY_TRACKER_TIER, ""},
+            {KEY_TRACKER_TIER, -1},
             {KEY_TRACKER_MSG, (isTorrentPrivate ? privateMsg : "")},
             {KEY_TRACKER_STATUS, ((BitTorrent::Session::instance()->isDHTEnabled() && !isTorrentPrivate) ? working : disabled)},
             {KEY_TRACKER_PEERS_COUNT, 0},
@@ -188,7 +188,7 @@ namespace
         const QJsonObject pex
         {
             {KEY_TRACKER_URL, "** [PeX] **"},
-            {KEY_TRACKER_TIER, ""},
+            {KEY_TRACKER_TIER, -1},
             {KEY_TRACKER_MSG, (isTorrentPrivate ? privateMsg : "")},
             {KEY_TRACKER_STATUS, ((BitTorrent::Session::instance()->isPeXEnabled() && !isTorrentPrivate) ? working : disabled)},
             {KEY_TRACKER_PEERS_COUNT, 0},
@@ -200,7 +200,7 @@ namespace
         const QJsonObject lsd
         {
             {KEY_TRACKER_URL, "** [LSD] **"},
-            {KEY_TRACKER_TIER, ""},
+            {KEY_TRACKER_TIER, -1},
             {KEY_TRACKER_MSG, (isTorrentPrivate ? privateMsg : "")},
             {KEY_TRACKER_STATUS, ((BitTorrent::Session::instance()->isLSDEnabled() && !isTorrentPrivate) ? working : disabled)},
             {KEY_TRACKER_PEERS_COUNT, 0},

src/webui/www/private/scripts/prop-trackers.js

@@ -97,7 +97,7 @@ window.qBittorrent.PropTrackers = (function() {
 
                         const row = {
                             rowId: tracker.url,
-                            tier: tracker.tier,
+                            tier: (tracker.tier >= 0) ? tracker.tier : "",
                             url: tracker.url,
                             status: status,
                             peers: tracker.num_peers,