Show error when image request fails

Signal/src/ViewControllers/PhotoLibrary/ImagePickerController.swift

@@ -317,10 +317,16 @@ class ImagePickerGridController: UICollectionViewController, PhotoLibraryDelegat
         let attachmentPromises: [Promise<SignalAttachment>] = assets.map({
             return photoCollectionContents.outgoingAttachment(for: $0)
         })
-        when(fulfilled: attachmentPromises)
-            .map { attachments in
+
+        firstly {
+            when(fulfilled: attachmentPromises)
+        }.map { attachments in
+            Logger.debug("built all attachments")
             self.didComplete(withAttachments: attachments)
-            }.retainUntilComplete()
+        }.catch { error in
+            Logger.error("failed to prepare attachments. error: \(error)")
+            OWSAlerts.showAlert(title: NSLocalizedString("IMAGE_PICKER_FAILED_TO_PROCESS_ATTACHMENTS", comment: "alert title"))
+        }.retainUntilComplete()
     }
 
     private func didComplete(withAttachments attachments: [SignalAttachment]) {

Signal/translations/en.lproj/Localizable.strings

@@ -1086,6 +1086,9 @@
 /* Label for crop button in image editor. */
 "IMAGE_EDITOR_CROP_BUTTON" = "Crop";
 
+/* alert title */
+"IMAGE_PICKER_FAILED_TO_PROCESS_ATTACHMENTS" = "Failed to select attachment.";
+
 /* Call setup status label */
 "IN_CALL_CONNECTING" = "Connecting…";
 
@@ -2402,9 +2405,6 @@
 /* Title for the alert indicating that user should upgrade iOS. */
 "UPGRADE_IOS_ALERT_TITLE" = "Upgrade iOS";
 
-/* No comment provided by engineer. */
-"Upgrading Signal ..." = "Upgrading Signal…";
-
 /* button text for back button on verification view */
 "VERIFICATION_BACK_BUTTON" = "Back";