Fix cancelling commands on <1.19 clients (#827)

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

@@ -743,14 +743,16 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                                                                          @Nullable SignedChatCommand signedCommand,
                                                                          Instant passedTimestamp) {
     IdentifiedKey playerKey = player.getIdentifiedKey();
-    if (result == CommandResult.denied() && playerKey != null) {
-      if (signedCommand != null && playerKey.getKeyRevision()
-          .compareTo(IdentifiedKey.Revision.LINKED_V2) >= 0) {
-        logger.fatal("A plugin tried to deny a command with signable component(s). "
-            + "This is not supported. "
-            + "Disconnecting player " + player.getUsername());
-        player.disconnect(Component.text("A proxy plugin caused an illegal protocol state. "
-            + "Contact your network administrator."));
+    if (result == CommandResult.denied()) {
+      if (playerKey != null) {
+        if (signedCommand != null && playerKey.getKeyRevision()
+            .compareTo(IdentifiedKey.Revision.LINKED_V2) >= 0) {
+          logger.fatal("A plugin tried to deny a command with signable component(s). "
+              + "This is not supported. "
+              + "Disconnecting player " + player.getUsername());
+          player.disconnect(Component.text("A proxy plugin caused an illegal protocol state. "
+              + "Contact your network administrator."));
+        }
       }
       return CompletableFuture.completedFuture(null);
     }