Fix crash when downloading attachment from S3.

app/src/main/java/org/thoughtcrime/securesms/database/AttachmentTable.kt

@@ -981,9 +981,10 @@ class AttachmentTable(
       limitStream.leftoverStream().allMatch { it == 0x00.toByte() }
     }
 
-    val digest = if (paddingAllZeroes) {
+    // Existing digest may be null for non-user attachments, like things pulled from S3
+    val digest = if (existingPlaceholder.remoteDigest != null && paddingAllZeroes) {
       Log.d(TAG, "[finalizeAttachmentAfterDownload] $attachmentId has all-zero padding. Digest is good.")
-      existingPlaceholder.remoteDigest!!
+      existingPlaceholder.remoteDigest
     } else {
       Log.w(TAG, "[finalizeAttachmentAfterDownload] $attachmentId has non-zero padding bytes. Recomputing digest.")
 

app/src/main/java/org/thoughtcrime/securesms/jobs/AttachmentDownloadJob.kt

@@ -416,11 +416,15 @@ class AttachmentDownloadJob private constructor(
           if (body.contentLength() > RemoteConfig.maxAttachmentReceiveSizeBytes) {
             throw MmsException("Attachment too large, failing download")
           }
+
+          SignalDatabase.attachments.createKeyIvIfNecessary(attachmentId)
+          val updatedAttachment = SignalDatabase.attachments.getAttachment(attachmentId)!!
+
           SignalDatabase.attachments.finalizeAttachmentAfterDownload(
             messageId,
             attachmentId,
             LimitedInputStream.withoutLimits((body.source() as Source).buffer().inputStream()),
-            iv = null
+            iv = updatedAttachment.remoteIv
           )
         }
       }