Simplify Swift invoice handling with non-optional return types

- Mentions.swift: convert_invoice_description now returns non-optional
  InvoiceDescription, returning empty description for BOLT11 compliance
  (both description and description_hash are optional per spec)

- Block.swift, NdbBlock.swift, NostrEvent.swift, NoteContent.swift:
  Updated call sites to use non-optional invoice conversion

- InvoiceTests.swift: Added test for specific failing invoice

Signed-off-by: alltheseas <alltheseas@noreply.github.com>
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

damus/Core/Nostr/Mentions.swift

@@ -294,16 +294,19 @@ func format_msats(_ msat: Int64, locale: Locale = Locale.current) -> String {
     return String(format: format, locale: locale, sats.decimalValue as NSDecimalNumber, formattedSats)
 }
 
-func convert_invoice_description(b11: ndb_invoice) -> InvoiceDescription? {
+/// Extracts the description from a BOLT11 invoice.
+/// Returns empty description if invoice has neither description nor description_hash,
+/// as both fields are optional per BOLT11 spec.
+func convert_invoice_description(b11: ndb_invoice) -> InvoiceDescription {
     if let desc = b11.description {
         return .description(String(cString: desc))
     }
-    
+
     if var deschash = maybe_pointee(b11.description_hash) {
         return .description_hash(Data(bytes: &deschash, count: 32))
     }
-    
-    return nil
+
+    return .description("")
 }
 
 func find_tag_ref(type: String, id: String, tags: [[String]]) -> Int? {

damus/Core/Nostr/NostrEvent.swift

@@ -839,9 +839,7 @@ func separate_invoices(ndb: Ndb, ev: NostrEvent, keypair: Keypair) -> [Invoice]?
         let invoiceBlocks: [Invoice] = (try? blockGroup.reduce(initialResult: [Invoice](), { index, invoices, block in
             switch block {
             case .invoice(let invoice):
-                if let invoice = invoice.as_invoice() {
-                    return .loopReturn(invoices + [invoice])
-                }
+                return .loopReturn(invoices + [invoice.as_invoice()])
             default:
                 break
             }

damus/Core/Types/Block.swift

@@ -79,8 +79,7 @@ extension Block {
             guard let url = URL(string: block.as_str()) else { return nil }
             self = .url(url)
         case BLOCK_INVOICE:
-            guard let b = Block(invoice: block.block.invoice) else { return nil }
-            self = b
+            self = Block(invoice: block.block.invoice)
         case BLOCK_MENTION_BECH32:
             guard let b = Block(bech32: block.block.mention_bech32) else { return nil }
             self = b
@@ -113,26 +112,20 @@ fileprivate extension Block {
 }
 
 fileprivate extension Block {
-    /// Failable initializer for the C-backed type `invoice_block_t`.
-    init?(invoice: ndb_invoice_block) {
-
-        guard let invoice = invoice_block_as_invoice(invoice) else { return nil }
-        self = .invoice(invoice)
+    /// Initializer for the C-backed type `invoice_block_t`.
+    init(invoice: ndb_invoice_block) {
+        self = .invoice(invoice_block_as_invoice(invoice))
     }
 }
 
-func invoice_block_as_invoice(_ invoice: ndb_invoice_block) -> Invoice? {
+/// Converts a C-backed invoice block to a Swift Invoice.
+func invoice_block_as_invoice(_ invoice: ndb_invoice_block) -> Invoice {
     let invstr = invoice.invstr.as_str()
     let b11 = invoice.invoice
-
-    guard let description = convert_invoice_description(b11: b11) else {
-        return nil
-    }
-
+    let description = convert_invoice_description(b11: b11)
     let amount: Amount = b11.amount == 0 ? .any : .specific(Int64(b11.amount))
 
     return Invoice(description: description, amount: amount, string: invstr, expiry: b11.expiry, created_at: b11.timestamp)
-
 }
 
 fileprivate extension Block {