CR: add comments, make atomic

// FREEBIE

SignalMessaging/Models/OWSQuotedReplyModel.h

@@ -37,6 +37,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)initWithQuotedMessage:(TSQuotedMessage *)quotedMessage
                           transaction:(YapDatabaseReadTransaction *)transaction;
 
+// Builds a not-yet-sent QuotedReplyModel
 + (nullable instancetype)quotedReplyForMessage:(TSMessage *)message
                                    transaction:(YapDatabaseReadTransaction *)transaction;
 

SignalServiceKit/src/Messages/Interactions/TSQuotedMessage.m

@@ -300,6 +300,7 @@ NS_ASSUME_NONNULL_BEGIN
     return [streamIds copy];
 }
 
+// Before sending, persist a thumbnail attachment derived from the quoted attachment
 - (NSArray<TSAttachmentStream *> *)createThumbnailAttachmentsIfNecessaryWithTransaction:
     (YapDatabaseReadWriteTransaction *)transaction
 {

SignalServiceKit/src/Util/OWSOperation.m

@@ -13,7 +13,7 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
 
 @interface OWSOperation ()
 
-@property (nonatomic) OWSOperationState operationState;
+@property (atomic) OWSOperationState operationState;
 @property (nonatomic) OWSBackgroundTask *backgroundTask;
 
 @end