avformat/dashdec: Check allocation of AVProgram

Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit aed96e13c1)

libavformat/dashdec.c

@@ -2120,6 +2120,7 @@ static int dash_read_header(AVFormatContext *s)
         AVProgram *program;
         program = av_new_program(s, 0);
         if (!program) {
+            ret = AVERROR(ENOMEM);
             goto fail;
         }