Avoid group-sync deadlock by making post-upload save async

// FREEBIE

SignalServiceKit/src/Network/API/OWSUploadingService.m

@@ -107,9 +107,7 @@ static const CGFloat kAttachmentUploadProgressTheta = 0.001f;
                                          DDLogInfo(@"%@ Uploaded attachment: %p.", self.tag, attachmentStream);
                                          attachmentStream.serverId = serverId;
                                          attachmentStream.isUploaded = YES;
-                                         [attachmentStream save];
-
-                                         successHandlerWrapper();
+                                         [attachmentStream saveAsyncWithCompletionBlock:successHandlerWrapper];
                                      }
                                      failure:failureHandlerWrapper];
 

SignalServiceKit/src/Storage/TSYapDatabaseObject.h

@@ -81,9 +81,10 @@
 + (instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID NS_SWIFT_NAME(fetch(uniqueId:));
 
 /**
- *  Saves the object with a new YapDatabaseConnection
+ *  Saves the object with shared readWrite connection.
  */
 - (void)save;
+- (void)saveAsyncWithCompletionBlock:(void (^_Nullable)(void))completionBlock;
 
 /**
  *  Saves the object with the provided transaction

SignalServiceKit/src/Storage/TSYapDatabaseObject.m

@@ -37,6 +37,14 @@
     }];
 }
 
+- (void)saveAsyncWithCompletionBlock:(void (^_Nullable)(void))completionBlock
+{
+    [[self dbReadWriteConnection] asyncReadWriteWithBlock:^(YapDatabaseReadWriteTransaction *_Nonnull transaction) {
+        [self saveWithTransaction:transaction];
+    }
+                                          completionBlock:completionBlock];
+}
+
 - (void)touchWithTransaction:(YapDatabaseReadWriteTransaction *)transaction
 {
     [transaction touchObjectForKey:self.uniqueId inCollection:[self.class collection]];