ObjC: Add null checks to HW encoder compressionOutputCallback

webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm

Index: webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm b/webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm
index a410e273cb602da06c3732dc658b88c92845b31f..0fcefeef0271d543c3976aee0c1e9f9dcac5e6f1 100644
--- a/webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm
+++ b/webrtc/sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm
@@ -148,8 +148,10 @@ void compressionOutputCallback(void *encoder,
                                OSStatus status,
                                VTEncodeInfoFlags infoFlags,
                                CMSampleBufferRef sampleBuffer) {
+  RTC_CHECK(params);
   std::unique_ptr<RTCFrameEncodeParams> encodeParams(
       reinterpret_cast<RTCFrameEncodeParams *>(params));
+  RTC_CHECK(encodeParams->encoder);
   [encodeParams->encoder frameWasEncoded:status
                                    flags:infoFlags
                             sampleBuffer:sampleBuffer