bus: Properly va_copy() argument list before passing it to printf() functions

As we later potentially use args again, we can't consume it with printf
functions without copying it first. Clone list before passing it to any
consuming function.

Fixes #621.

src/libcharon/bus/bus.c

@@ -391,7 +391,9 @@ METHOD(bus_t, vlog, void,
 		{
 			len++;
 			data.message = malloc(len);
-			len = vsnprintf(data.message, len, format, args);
+			va_copy(data.args, args);
+			len = vsnprintf(data.message, len, format, data.args);
+			va_end(data.args);
 		}
 		if (len > 0)
 		{