fix: Clear draft when leaving a group or when Self is removed.

Fix #6175.

This is not a very bad bug (even WhatsApp has the same bug, and WhatsApp
rarely has any bugs at all!), so I think it's fine not to add regression
tests.

I did test that it works on an Android phone. Clearing the draft when a
different device leaves the group or when Self is removed from the group
works.

What doesn't work is clearing the draft when leaving a group from this
device, because after leaving, the UI still has the draft in the
now-hidden input bar, and calls set_draft() when the user leaves the
activity, re-adding the draft. We could fix this by loading the chat in
do_set_draft(), calling, `is_self_in_chat()`, and not setting the draft
if self isn't in the chat. This is two extra database calls everytime
the user leaves a group and goes back to the chat list - not a big
deal, but I'm nonetheless not sure it's worth it for this super arcane
bug. What do you think?

src/chat.rs

@@ -3921,6 +3921,11 @@ pub async fn remove_contact_from_chat(
     let mut msg = Message::default();
 
     let chat = Chat::load_from_db(context, chat_id).await?;
+
+    if chat.typ == Chattype::Group && contact_id == ContactId::SELF {
+        chat_id.set_draft(context, None).await?; // Clear draft since the user left the group.
+    }
+
     if chat.typ == Chattype::Group || chat.typ == Chattype::Broadcast {
         if !chat.is_self_in_chat(context).await? {
             let err_msg = format!(
@@ -4611,6 +4616,11 @@ async fn set_contacts_by_addrs(context: &Context, id: ChatId, addrs: &[String])
     if contacts == contacts_old {
         return Ok(());
     }
+
+    if chat.typ == Chattype::Group && !contacts.contains(&ContactId::SELF) {
+        id.set_draft(context, None).await?; // Clear draft since the user left the group.
+    }
+
     update_chat_contacts_table(context, id, &contacts).await?;
     context.emit_event(EventType::ChatModified(id));
     Ok(())

src/receive_imf.rs

@@ -2317,6 +2317,9 @@ async fn apply_group_changes(
         }
 
         if new_members != chat_contacts {
+            if !new_members.contains(&ContactId::SELF) {
+                chat_id.set_draft(context, None).await?; // Clear draft since Self was removed from the group.
+            }
             chat::update_chat_contacts_table(context, chat_id, &new_members).await?;
             chat_contacts = new_members;
             send_event_chat_modified = true;