avformat/latmenc: abort if no extradata is available

Fixes ticket #8273.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit dd01947397)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/latmenc.c

@@ -172,7 +172,8 @@ static int latm_write_packet(AVFormatContext *s, AVPacket *pkt)
                 if (ret < 0)
                     return ret;
                 memcpy(par->extradata, side_data, side_data_size);
-            }
+            } else
+                return AVERROR_INVALIDDATA;
         }
     }