Switch audio source if audio-dup is set

Automatically switch implicit audio source to "playback" if --audio-dup
is passed.

This allows to run:

    scrcpy --audio-dup

without specifying explicitly:

    scrcpy --audio-source=playback --audio-dup

PR #5102 <#5102>

app/src/cli.c

@@ -2895,7 +2895,13 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
     if (opts->audio && opts->audio_source == SC_AUDIO_SOURCE_AUTO) {
         // Select the audio source according to the video source
         if (opts->video_source == SC_VIDEO_SOURCE_DISPLAY) {
-            opts->audio_source = SC_AUDIO_SOURCE_OUTPUT;
+            if (opts->audio_dup) {
+                LOGI("Audio duplication enabled: audio source switched to "
+                     "\"playback\"");
+                opts->audio_source = SC_AUDIO_SOURCE_PLAYBACK;
+            } else {
+                opts->audio_source = SC_AUDIO_SOURCE_OUTPUT;
+            }
         } else {
             opts->audio_source = SC_AUDIO_SOURCE_MIC;
             LOGI("Camera video source: microphone audio source selected");