Fix DiscordAPIError on receiving empty content.

Previously, when OpenAI returned a message with an empty string,
it would try to send that empty message, which throwed an error.

Now it will react with an emoji to the message that triggered the request.

src/index.ts

@@ -39,20 +39,27 @@ discord.on("messageCreate", async message => {
       max_tokens: 168
     });
 
-    const response = message.reply({
-      content: answer.data.choices[0].message?.content,
-      allowedMentions: {
-        repliedUser: false,
-      }
-    });
-
     const usage = answer.data.usage;
     if (usage != undefined) {
       const channelName: string = message.inGuild() ? `${message.channel.name} (${message.guild.name})` : `@${message.author.tag}`;
       console.log(`Used ${usage.total_tokens} (${usage.prompt_tokens} + ${usage.completion_tokens}) tokens for ${message.author.tag} (${message.author.id}) in #${channelName}`);
     }
 
-    Moderation.checkMessage(await response);
+    const answerContent = answer.data.choices[0].message?.content;
+
+    if (answerContent != undefined && answerContent != "") {
+      const response = message.reply({
+        content: answerContent,
+        allowedMentions: {
+          repliedUser: false,
+        }
+      });
+
+      Moderation.checkMessage(await response);
+    }
+    else {
+      message.react("😶");
+    }
   } catch (e) {
     console.error(e);