avformat/webvttenc: Fix use of uninitialized variable

Happened in 9168a1c0e6.

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/webvttenc.c

@@ -87,7 +87,7 @@ static int webvtt_write_packet(AVFormatContext *ctx, AVPacket *pkt)
     settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
                                        &settings_size);
 
-    if (settings_size_int > INT_MAX)
+    if (settings_size > INT_MAX)
         return AVERROR(EINVAL);
 
     settings_size_int = settings_size;