doc/examples/qsv_transcode: Initialize pointer before free

Fixees: CID1517023 Uninitialized pointer read

Sponsored-by: Sovereign Tech Fund
Reviewed-by: "Xiang, Haihao" <haihao.xiang@intel.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit cae0f2bc55)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/examples/qsv_transcode.c

@@ -341,7 +341,7 @@ int main(int argc, char **argv)
 {
     const AVCodec *enc_codec;
     int ret = 0;
-    AVPacket *dec_pkt;
+    AVPacket *dec_pkt = NULL;
 
     if (argc < 5 || (argc - 5) % 2) {
         av_log(NULL, AV_LOG_ERROR, "Usage: %s <input file> <encoder> <output file>"