fix skipped write_index

nodes/decklink-in/src/decklink_in_node.cpp

@@ -175,16 +175,20 @@ void DeckLinkInNode::process() {
 
     {
         std::lock_guard<std::mutex> lock(frame_mutex_);
-        if (!frame_ready_ || !frame_data_) {
-            return;
-        }
+        if (frame_data_) {
             src_data = frame_data_;
             src_row_bytes = frame_row_bytes_;
             src_width = frame_width_;
             src_height = frame_height_;
+        }
         frame_ready_ = false;
     }
 
+    if (!src_data) {
+        write_index_++;
+        return;
+    }
+
     mxlGrainInfo out_grain{};
     uint8_t* out_payload = nullptr;
     auto status = mxlFlowWriterOpenGrain(*writer_, write_index_, &out_grain, &out_payload);