Several minor improvements of DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc

Index: webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
diff --git a/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc b/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
index d7eb335fc3cf1e193da07b977424a38920b2fe6f..987fbebbb916a27cb093b6700850d2bd31d24f89 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
+++ b/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
@@ -18,6 +18,7 @@
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h"
 #include "webrtc/modules/desktop_capture/win/dxgi_texture_mapping.h"
 #include "webrtc/modules/desktop_capture/win/dxgi_texture_staging.h"
 
@@ -147,7 +148,9 @@ bool DxgiOutputDuplicator::Duplicate(Context* context,
   // after it has been merged to updated_region.
   DesktopRegion updated_region;
   updated_region.Swap(&context->updated_region);
-  if (error.Error() == S_OK && frame_info.AccumulatedFrames > 0) {
+  if (error.Error() == S_OK &&
+      frame_info.AccumulatedFrames > 0 &&
+      resource) {
     DetectUpdatedRegion(frame_info, offset, &context->updated_region);
     if (!texture_->CopyFrom(frame_info, resource.Get(),
                             context->updated_region)) {