Possibly fix wrong requests order.

Telegram/SourceFiles/mtproto/mtp_instance.cpp

@@ -1020,11 +1020,24 @@ void Instance::Private::sendRequest(
 	const auto signedDcId = toMainDc ? -realShiftedDcId : realShiftedDcId;
 	registerRequest(requestId, signedDcId);
 
+	request->lastSentTime = crl::now();
+	request->needsLayer = needsLayer;
+
 	if (afterRequestId) {
 		request->after = getRequest(afterRequestId);
+
+		if (request->after) {
+			// Check if this after request is waiting in _dependentRequests.
+			// This happens if it was after some other request and failed
+			// to wait for it, but that other request is still processed.
+			QMutexLocker locker(&_dependentRequestsLock);
+			const auto i = _dependentRequests.find(afterRequestId);
+			if (i != end(_dependentRequests)) {
+				_dependentRequests.emplace(requestId, afterRequestId);
+				return;
+			}
+		}
 	}
-	request->lastSentTime = crl::now();
-	request->needsLayer = needsLayer;
 
 	session->sendPrepared(request, msCanWait);
 }