output_all: clear input_audio_format on close

When the audio outputs are closed, also clear the audio format.  If we
don't do this, every call to audio_output_all_update() will open the
device, even if it's meant to be paused.

src/output_all.c

@@ -443,4 +443,6 @@ audio_output_all_close(void)
 	}
 
 	g_music_buffer = NULL;
+
+	audio_format_clear(&input_audio_format);
 }