Verify FFmpeg diagnostic callback restoration

tools/chatgui/src/live_video_encoder.cpp

@@ -3,6 +3,7 @@
 #include <QElapsedTimer>
 #include <QPainter>
 #include <algorithm>
+#include <cstdlib>
 #include <cstring>
 #include <deque>
 extern "C" {

tools/chatgui/tests/test_stream_publish.cpp

@@ -227,6 +227,10 @@ private slots:
         av_log(context, AV_LOG_DEBUG, "UTUN_AMF_LOG_TEST Warning: AMFEncoderUVEHEVCImpl::QueryOutput() failed\n");
         QCOMPARE(ffmpegDiagnosticMessages.size(), 3);
         QVERIFY(ffmpegDiagnosticMessages.back().contains("Warning:"));
+        av_log_set_callback(av_log_default_callback); video_ffmpeg_init();
+        av_log(context, AV_LOG_DEBUG, "UTUN_AMF_LOG_TEST callback restored\n");
+        QCOMPARE(ffmpegDiagnosticMessages.size(), 4);
+        QVERIFY(ffmpegDiagnosticMessages.back().contains("callback restored"));
 #else
         QSKIP("FFmpeg unavailable");
 #endif