melib/imap: on set_flags, update {un,}seen sets in all mailboxes

Some envelopes might be in several mailboxes, for example in Gmail's
implementation of IMAP.

melib/src/backends/imap.rs

@@ -793,7 +793,7 @@ impl MailBackend for ImapType {
                 conn.read_response(&mut response, RequiredResponses::empty())
                     .await?;
                 if set_seen {
-                    let f = &uid_store.mailboxes.lock().await[&mailbox_hash];
+                    for f in uid_store.mailboxes.lock().await.values() {
                         if let Ok(mut unseen) = f.unseen.lock() {
                             for env_hash in env_hashes.iter() {
                                 unseen.remove(env_hash);
@@ -801,6 +801,7 @@ impl MailBackend for ImapType {
                         };
                     }
                 }
+            }
             if flags.iter().any(|(_, b)| !*b) {
                 let mut set_unseen = false;
                 /* Set flags/tags to false */
@@ -858,7 +859,7 @@ impl MailBackend for ImapType {
                 conn.read_response(&mut response, RequiredResponses::empty())
                     .await?;
                 if set_unseen {
-                    let f = &uid_store.mailboxes.lock().await[&mailbox_hash];
+                    for f in uid_store.mailboxes.lock().await.values() {
                         if let Ok(mut unseen) = f.unseen.lock() {
                             for env_hash in env_hashes.iter() {
                                 unseen.insert_new(env_hash);
@@ -866,6 +867,7 @@ impl MailBackend for ImapType {
                         };
                     }
                 }
+            }
             Ok(())
         }))
     }