Merge pull request opencv#25419 from vrabaud:ffmpeg

Fix race condition in InternalFFMpegRegister initialization. opencv#25419

initLogger_ does not check if the logger has been initizalized before and it might initialize it several times from different threads, racing with other threads that are logging.

### 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
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work

modules/videoio/src/cap_ffmpeg_impl.hpp

@@ -927,7 +927,6 @@ class InternalFFMpegRegister
         if(!threadSafe)
             lock.lock();
         static InternalFFMpegRegister instance;
-        initLogger_();  // update logger setup unconditionally (GStreamer's libav plugin may override these settings)
     }
     static void initLogger_()
     {
@@ -965,6 +964,7 @@ class InternalFFMpegRegister
         /* register a callback function for synchronization */
         av_lockmgr_register(&LockCallBack);
 #endif
+        initLogger_();
     }
     ~InternalFFMpegRegister()
     {