Fix #7459, empty attachment arrays causing errors when updating the message

packages/rocketchat-lib/server/methods/updateMessage.js

@@ -39,12 +39,11 @@ Meteor.methods({
 			}
 		}
 
-		if (originalMessage.attachments) {
-			if (originalMessage.attachments[0].description !== undefined) {
-				message.attachments = originalMessage.attachments;
-				message.attachments[0].description = message.msg;
-				message.msg = originalMessage.msg;
-			}
+		// It is possible to have an empty array as the attachments property, so ensure both things exist
+		if (originalMessage.attachments && originalMessage.attachments.length > 0 && originalMessage.attachments[0].description !== undefined) {
+			message.attachments = originalMessage.attachments;
+			message.attachments[0].description = message.msg;
+			message.msg = originalMessage.msg;
 		}
 
 		message.u = originalMessage.u;