Connectivity view: Only set smtp to "connected" if the last message was actually sent (#2541)

fix #2539

It's always a bit ambiguous which function should do set_err or set last_send_error, I used this rule here:

If some code returns Status::RetryLater, then it sets last_send_error, because Status::RetryLater means that the user won't see the error directly on the message (if we returned Status::Failed(Err(_)), then the message would be shown as failed to the user) Also, smtp_send always sets last_send_error because, well, sending just failed or succeeded.

Also, remove unused field pending_error.

src/smtp.rs

@@ -54,6 +54,9 @@ pub(crate) struct Smtp {
     last_success: Option<SystemTime>,
 
     pub(crate) connectivity: ConnectivityStore,
+
+    /// If sending the last message failed, contains the error message.
+    pub(crate) last_send_error: Option<String>,
 }
 
 impl Smtp {
@@ -100,20 +103,14 @@ impl Smtp {
 
         self.connectivity.set_connecting(context).await;
         let lp = LoginParam::from_database(context, "configured_").await?;
-        let res = self
-            .connect(
-                context,
-                &lp.smtp,
-                &lp.addr,
-                lp.server_flags & DC_LP_AUTH_OAUTH2 != 0,
-                lp.provider.map_or(false, |provider| provider.strict_tls),
-            )
-            .await;
-
-        if let Err(err) = &res {
-            self.connectivity.set_err(context, err).await;
-        }
-        res
+        self.connect(
+            context,
+            &lp.smtp,
+            &lp.addr,
+            lp.server_flags & DC_LP_AUTH_OAUTH2 != 0,
+            lp.provider.map_or(false, |provider| provider.strict_tls),
+        )
+        .await
     }
 
     /// Connect using the provided login params.