Fix TabList population

Bug reported by JakubBien on Discord

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -211,7 +211,8 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(PlayerListItem packet) {
-    return !serverConn.getPlayer().getTabList().processBackendPacket(packet);
+    serverConn.getPlayer().getTabList().processBackendPacket(packet);
+    return false;
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/tablist/VelocityTabList.java

@@ -129,9 +129,8 @@ public class VelocityTabList implements TabList {
    * Processes a tab list entry packet from the backend.
    *
    * @param packet the packet to process
-   * @return {@code true} to forward the packet on, {@code false} otherwise
    */
-  public boolean processBackendPacket(PlayerListItem packet) {
+  public void processBackendPacket(PlayerListItem packet) {
     // Packets are already forwarded on, so no need to do that here
     for (PlayerListItem.Item item : packet.getItems()) {
       UUID uuid = item.getUuid();
@@ -150,13 +149,13 @@ public class VelocityTabList implements TabList {
           if (name == null || properties == null) {
             throw new IllegalStateException("Got null game profile for ADD_PLAYER");
           }
-          return entries.putIfAbsent(item.getUuid(), (VelocityTabListEntry) TabListEntry.builder()
+          entries.putIfAbsent(item.getUuid(), (VelocityTabListEntry) TabListEntry.builder()
               .tabList(this)
               .profile(new GameProfile(uuid, name, properties))
               .displayName(item.getDisplayName())
               .latency(item.getLatency())
               .gameMode(item.getGameMode())
-              .build()) == null;
+              .build());
         }
         case PlayerListItem.REMOVE_PLAYER:
           entries.remove(uuid);
@@ -187,7 +186,6 @@ public class VelocityTabList implements TabList {
           break;
       }
     }
-    return true;
   }
 
   void updateEntry(int action, TabListEntry entry) {

proxy/src/main/java/com/velocitypowered/proxy/tablist/VelocityTabListLegacy.java

@@ -72,7 +72,7 @@ public class VelocityTabListLegacy extends VelocityTabList {
   }
 
   @Override
-  public boolean processBackendPacket(PlayerListItem packet) {
+  public void processBackendPacket(PlayerListItem packet) {
     Item item = packet.getItems().get(0); // Only one item per packet in 1.7
 
     switch (packet.getAction()) {
@@ -102,8 +102,6 @@ public class VelocityTabListLegacy extends VelocityTabList {
         // For 1.7 there is only add and remove
         break;
     }
-
-    return true;
   }
 
   @Override