Merge pull request #27737 from cudawarped:fix_videowriter_raw_return_code

[videoio][VideoWriter] Fix return code from CvVideoWriter_FFMPEG::writeFrame() when encapsulating encoded video #27737

Currently the return code from `CvVideoWriter_FFMPEG::writeFrame()` when `encode_video==true` (encapsulating raw encoded video) is wrong and results in the following warning implying it has been unsuccessful

> [ WARN:0@15.551] global cap_ffmpeg.cpp:198 write FFmpeg: Failed to write frame

### Pull Request Readiness Checklist

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- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [ ] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/videoio/src/cap_ffmpeg_impl.hpp

@@ -2531,9 +2531,9 @@ bool CvVideoWriter_FFMPEG::writeFrame( const unsigned char* data, int step, int
     if (!encode_video) {
         CV_Assert(cn == 1 && ((width > 0 && height == 1) || (width == 1 && height > 0 && step == 1)));
         const bool set_key_frame = key_frame ? key_frame : idr_period ? frame_idx % idr_period == 0 : 1;
-        bool ret = icv_av_encapsulate_video_FFMPEG(oc, video_st, context, (uint8_t*)data, width, frame_idx, pts_index, b_frame_dts_delay, set_key_frame);
+        int ret = icv_av_encapsulate_video_FFMPEG(oc, video_st, context, (uint8_t*)data, width, frame_idx, pts_index, b_frame_dts_delay, set_key_frame);
         frame_idx++;
-        return ret;
+        return ret == 0;
     }
 
     // check parameters