libwebpenc_animencoder: add missing braces to struct initialization

The first member of the WebPAnimEncoderOptions struct is non scalar
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/libwebpenc_animencoder.c

@@ -41,7 +41,7 @@ static av_cold int libwebp_anim_encode_init(AVCodecContext *avctx)
     int ret = ff_libwebp_encode_init_common(avctx);
     if (!ret) {
         LibWebPAnimContext *s = avctx->priv_data;
-        WebPAnimEncoderOptions enc_options = { 0 };
+        WebPAnimEncoderOptions enc_options = { { 0 } };
         WebPAnimEncoderOptionsInit(&enc_options);
         enc_options.verbose = av_log_get_level() >= AV_LOG_VERBOSE;
         // TODO(urvang): Expose some options on command-line perhaps.