fix: handle non-iterable messageInfo.attachments in mailbox sync

Add defensive || [] fallback when iterating over messageInfo.attachments
to prevent TypeError when attachments is undefined or null. This fixes
crashes during processNew, publishSyncedEvents, and other sync operations
when processing messages without attachments.

Affected locations:
- ARF complaint attachment download (line 780)
- Inline attachment fetching (line 1088)
- CID-referenced attachment collection (lines 1380, 2317)

Author: andris9

lib/email-client/imap/mailbox.js

@@ -777,7 +777,7 @@ class Mailbox {
         if (this.mightBeAComplaint(messageInfo)) {
             try {
                 // Download relevant attachments for ARF parsing
-                for (let attachment of messageInfo.attachments) {
+                for (let attachment of messageInfo.attachments || []) {
                     if (!['message/feedback-report', 'message/rfc822-headers', 'message/rfc822'].includes(attachment.contentType)) {
                         continue;
                     }
@@ -1085,7 +1085,7 @@ class Mailbox {
         // Fetch inline attachments referenced in HTML
         if (messageInfo.attachments?.length && messageInfo.text?.html) {
             // fetch inline attachments
-            for (let attachment of messageInfo.attachments) {
+            for (let attachment of messageInfo.attachments || []) {
                 if (attachment.encodedSize && attachment.encodedSize > MAX_INLINE_ATTACHMENT_SIZE) {
                     // skip large attachments
                     continue;
@@ -1377,7 +1377,7 @@ class Mailbox {
                 let partList = [];
 
                 // Collect CID-referenced attachments
-                for (let attachment of messageInfo.attachments) {
+                for (let attachment of messageInfo.attachments || []) {
                     let contentId = attachment.contentId && attachment.contentId.replace(/^<|>$/g, '');
                     if (contentId && messageInfo.text.html.indexOf(contentId) >= 0) {
                         attachmentList.set(contentId, {
@@ -2314,7 +2314,7 @@ class Mailbox {
                 let partList = [];
 
                 // Find images referenced by CID
-                for (let attachment of messageInfo.attachments) {
+                for (let attachment of messageInfo.attachments || []) {
                     let contentId = attachment.contentId && attachment.contentId.replace(/^<|>$/g, '');
                     if (contentId && messageInfo.text.html.indexOf(contentId) >= 0) {
                         attachmentList.set(contentId, { attachment, content: null });