printf-hook-builtin: Correctly calculate written bytes in print_in_hook()

The hook data counts remaining buffer bytes, not used ones. Counting them
correctly fixes a crash for long hexdumps.

Further, print_in_hook() must return the number of bytes that would have been
written, not the actually written bytes. This is important, as we allocate a
dynamic buffer in bus that relies on the exact byte count. Fixes long hexdumps
that got truncated.

src/libstrongswan/utils/printf_hook/printf_hook_builtin.c

@@ -122,10 +122,14 @@ size_t print_in_hook(printf_hook_data_t *data, char *fmt, ...)
 
 	if (written > data->n)
 	{
-		written = data->n;
+		data->q += data->n;
+		data->n = 0;
+	}
+	else
+	{
+		data->q += written;
+		data->n -= written;
 	}
-	data->q += written;
-	data->n += written;
 	return written;
 }