refactor(unremind): return an error when a user tries to delete a reminder that has already been completed

Author: Akinator31

crates/rustmail/src/commands/remove_reminder/slash_command/remove_reminder.rs

@@ -100,7 +100,15 @@ impl RegistrableCommand for RemoveReminderCommand {
             };
 
             let reminder = match get_reminder_by_id(reminder_id, pool).await {
-                Ok(Some(r)) => r,
+                Ok(Some(r)) => {
+                    if r.completed {
+                        return Err(ModmailError::Command(
+                            CommandError::ReminderAlreadyCompleted(reminder_id.to_string()),
+                        ));
+                    } else {
+                        r
+                    }
+                }
                 Ok(None) => {
                     return Err(ModmailError::Database(DatabaseError::NotFound(
                         "".to_string(),

crates/rustmail/src/commands/remove_reminder/text_command/remove_reminder.rs

@@ -38,7 +38,15 @@ pub async fn remove_reminder(
     };
 
     let reminder = match get_reminder_by_id(reminder_id as i64, pool).await {
-        Ok(Some(r)) => r,
+        Ok(Some(r)) => {
+            if r.completed {
+                return Err(ModmailError::Command(
+                    CommandError::ReminderAlreadyCompleted(reminder_id.to_string()),
+                ));
+            } else {
+                r
+            }
+        }
         Ok(None) => {
             return Err(ModmailError::Database(DatabaseError::NotFound(
                 "".to_string(),