fix: get boardChannel from Optional

By the time we need to get the contents of boardChannel when we attempt
to insert the cool message, the boardChannel's optional will never be
empty, so use Optional#get() instead.

Author: christolis

application/src/main/java/org/togetherjava/tjbot/features/basic/CoolMessagesBoardManager.java

@@ -65,7 +65,7 @@ public void onMessageReactionAdd(MessageReactionAddEvent event) {
             event.retrieveMessage().queue(message -> {
                 message.addReaction(REACT_EMOJI).queue();
 
-                insertCoolMessage(boardChannel.orElseThrow(), message);
+                insertCoolMessage(boardChannel.get(), message);
             }, e -> logger.warn("Tried to retrieve cool message but got: {}", e.getMessage()));
         }
     }