Sanity: reset ping ID after getting the right KeepAlive

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

@@ -208,4 +208,8 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
         this.lastPingId = lastPingId;
         this.lastPingSent = System.currentTimeMillis();
     }
+
+    public void resetLastPingId() {
+        this.lastPingId = -1;
+    }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -69,6 +69,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             }
             player.setPing(System.currentTimeMillis() - serverConnection.getLastPingSent());
             serverConnection.getMinecraftConnection().write(packet);
+            serverConnection.resetLastPingId();
             return;
         }