message: bubble up SQL errors in handle_mdn()

Previously handle_mdn() returned Ok(None) in response to SQL errors as
if SQL simply returned no rows.

src/message.rs

@@ -1644,7 +1644,7 @@ pub async fn handle_mdn(
 
     let res = context
         .sql
-        .query_row(
+        .query_row_optional(
             concat!(
                 "SELECT",
                 "    m.id AS msg_id,",
@@ -1665,14 +1665,20 @@ pub async fn handle_mdn(
                 ))
             },
         )
-        .await;
-    if let Err(ref err) = res {
-        info!(context, "Failed to select MDN {:?}", err);
-    }
+        .await?;
+
+    let (msg_id, chat_id, chat_type, msg_state) = if let Some(res) = res {
+        res
+    } else {
+        info!(
+            context,
+            "handle_mdn found no message with Message-ID {:?} sent by us in the database",
+            rfc724_mid
+        );
+        return Ok(None);
+    };
 
-    if let Ok((msg_id, chat_id, chat_type, msg_state)) = res {
     let mut read_by_all = false;
-
     if msg_state == MessageState::OutPreparing
         || msg_state == MessageState::OutPending
         || msg_state == MessageState::OutDelivered
@@ -1687,7 +1693,9 @@ pub async fn handle_mdn(
             .unwrap_or_default();
 
         if !mdn_already_in_table {
-                context.sql.execute(
+            context
+                .sql
+                .execute(
                     "INSERT INTO msgs_mdns (msg_id, contact_id, timestamp_sent) VALUES (?, ?, ?);",
                     paramsv![msg_id, from_id as i32, timestamp_sent],
                 )
@@ -1727,13 +1735,12 @@ pub async fn handle_mdn(
             } // else wait for more receipts
         }
     }
-        return if read_by_all {
+
+    if read_by_all {
         Ok(Some((chat_id, msg_id)))
     } else {
         Ok(None)
-        };
     }
-    Ok(None)
 }
 
 /// Marks a message as failed after an ndn (non-delivery-notification) arrived.