decoder/ffmpeg: fix crash on startup in mpd_ffmpeg_log_callback()

What's happening is the `ptr' argument to that function is NULL for me every time. `ptr' is unconditionally dereferenced to generate a log message, and this is where mpd crashes. Attached is a simple patch that tests for NULL and omits the log. With this patch the crash disappeared and mpd went back to working well.

decoder/ffmpeg: fix crash on startup in mpd_ffmpeg_log_callback()
6a958980 · Charles Kerr · Max Kellermann · c52f469c · 6a958980
Commit 6a958980 authored Apr 11, 2010 by Charles Kerr Committed by Max Kellermann Apr 11, 2010
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ffmpeg_decoder_plugin.c src/decoder/ffmpeg_decoder_plugin.c +9 -4

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--- a/src/decoder/ffmpeg_decoder_plugin.c
+++ b/src/decoder/ffmpeg_decoder_plugin.c
@@ -67,11 +67,16 @@ static void
 mpd_ffmpeg_log_callback(G_GNUC_UNUSED void *ptr, int level,
 			const char *fmt, va_list vl)
 {
-	const AVClass *cls = *(const AVClass *const*)ptr;
-	char *domain = g_strconcat(G_LOG_DOMAIN, "/", cls->item_name(ptr), NULL);
+	const AVClass * cls = NULL;

-	g_logv(domain, level_ffmpeg_to_glib(level), fmt, vl);
-	g_free(domain);
+	if (ptr != NULL)
+		cls = *(const AVClass *const*)ptr;
+
+	if (cls != NULL) {
+		char *domain = g_strconcat(G_LOG_DOMAIN, "/", cls->item_name(ptr), NULL);
+		g_logv(domain, level_ffmpeg_to_glib(level), fmt, vl);
+		g_free(domain);
+	}
 }

 #endif /* !OLD_FFMPEG_INCLUDES */