Update to latest Backup.proto and fix various backup bugs.

app/src/main/java/org/thoughtcrime/securesms/attachments/ArchivedAttachment.kt

@@ -49,13 +49,14 @@ class ArchivedAttachment : Attachment {
     stickerLocator: StickerLocator?,
     gif: Boolean,
     quote: Boolean,
-    uuid: UUID?
+    uuid: UUID?,
+    fileName: String?
   ) : super(
     contentType = contentType ?: "",
     quote = quote,
     transferState = AttachmentTable.TRANSFER_NEEDS_RESTORE,
     size = size,
-    fileName = null,
+    fileName = fileName,
     cdn = Cdn.fromCdnNumber(cdn),
     remoteLocation = cdnKey,
     remoteKey = Base64.encodeWithoutPadding(key),

app/src/main/java/org/thoughtcrime/securesms/attachments/Cdn.kt

@@ -46,7 +46,7 @@ enum class Cdn(private val value: Int) {
         0 -> CDN_0
         2 -> CDN_2
         3 -> CDN_3
-        else -> throw UnsupportedOperationException()
+        else -> throw UnsupportedOperationException("Invalid CDN number: $cdnNumber")
       }
     }
   }

app/src/main/java/org/thoughtcrime/securesms/attachments/DatabaseAttachment.kt

@@ -83,7 +83,7 @@ class DatabaseAttachment : Attachment {
     thumbnailRestoreState: AttachmentTable.ThumbnailRestoreState,
     uuid: UUID?
   ) : super(
-    contentType = contentType!!,
+    contentType = contentType,
     transferState = transferProgress,
     size = size,
     fileName = fileName,

app/src/main/java/org/thoughtcrime/securesms/attachments/TombstoneAttachment.kt

@@ -13,7 +13,7 @@ import java.util.UUID
  * quote them and know their contentType even though the media has been deleted.
  */
 class TombstoneAttachment : Attachment {
-  constructor(contentType: String, quote: Boolean) : super(
+  constructor(contentType: String?, quote: Boolean) : super(
     contentType = contentType,
     quote = quote,
     transferState = AttachmentTable.TRANSFER_PROGRESS_DONE,

app/src/main/java/org/thoughtcrime/securesms/attachments/UriAttachment.kt

@@ -14,7 +14,7 @@ class UriAttachment : Attachment {
 
   constructor(
     uri: Uri,
-    contentType: String,
+    contentType: String?,
     transferState: Int,
     size: Long,
     fileName: String?,
@@ -50,7 +50,7 @@ class UriAttachment : Attachment {
   @JvmOverloads
   constructor(
     dataUri: Uri,
-    contentType: String,
+    contentType: String?,
     transferState: Int,
     size: Long,
     width: Int,