fix: VideoReader crash on video-only file at EOF and dead bool return

- Guard swr_close/swr_init at EOF inside if (has_audio) — calling
  swr_init(nullptr) on a video-only file crashed at first loop
- Change open_file from bool to void — it never returned false, only
  threw, so the if (!open_file()) check in the constructor was dead code

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

shared/VideoReader.hpp

@@ -41,9 +41,7 @@ public:
     bool has_video = false;
 
     explicit VideoReader(const std::string& filename) {
-        if (!open_file(filename))
-            return;
-        if (!has_video && !has_audio) return;
+        open_file(filename);
         get_source_info();
         if (has_video) allocate_video_conversion_buffers();
         if (has_audio)  allocate_audio_conversion_buffers();
@@ -134,9 +132,11 @@ public:
                 // EOF — loop back to start
                 avformat_seek_file(format_context, -1, 0, 0, 0, AVSEEK_FLAG_BACKWARD);
                 if (has_video) avcodec_flush_buffers(video_codec_context);
-                if (has_audio) avcodec_flush_buffers(audio_codec_context);
-                swr_close(swr_audio_ctx);
-                swr_init(swr_audio_ctx);
+                if (has_audio) {
+                    avcodec_flush_buffers(audio_codec_context);
+                    swr_close(swr_audio_ctx);
+                    swr_init(swr_audio_ctx);
+                }
                 continue;
             }
 
@@ -166,7 +166,7 @@ private:
     AVFrame*        audio_frame        = av_frame_alloc();
     SwrContext* swr_audio_ctx = nullptr;
 
-    bool open_file(const std::string& filename) {
+    void open_file(const std::string& filename) {
         if (avformat_open_input(&format_context, filename.c_str(), nullptr, nullptr) != 0)
             throw std::runtime_error("Could not open file: " + filename);
 
@@ -186,12 +186,10 @@ private:
             }
         }
 
-        if (video_stream_index == -1 && audio_stream_index == -1) {
+        if (!has_video && !has_audio) {
             avformat_close_input(&format_context);
             throw std::runtime_error("No audio/video stream found in: " + filename);
         }
-
-        return true;
     }
 
     void get_source_info() {