CR: use id for hashvalue, make clearer that we don't expect to use incrementing ID's for uniqueId

Signal/src/ViewControllers/MediaGalleryViewController.swift

@@ -45,7 +45,7 @@ public class MediaGalleryItem: Equatable, Hashable {
     // MARK: Hashable
 
     public var hashValue: Int {
-        return attachmentStream.hashValue
+        return attachmentStream.uniqueId?.hashValue ?? attachmentStream.hashValue
     }
 }
 

SignalServiceKit/src/Messages/Interactions/TSInteraction.m

@@ -172,8 +172,8 @@ NSString *NSStringFromOWSInteractionType(OWSInteractionType value)
 }
 
 - (void)saveWithTransaction:(YapDatabaseReadWriteTransaction *)transaction {
-    OWSAssertDebug(self.uniqueId);
     if (!self.uniqueId) {
+        OWSFailDebug(self.uniqueId);
         self.uniqueId = [OWSPrimaryStorage getAndIncrementMessageIdWithTransaction:transaction];
     }