demux: mp4: fix heap read overflow in vide handler

(cherry picked from commit 3417a40402599d56395fd2ae0e55baec25e41a52)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mp4/libmp4.c

@@ -1825,6 +1825,8 @@ int MP4_ReadBox_sample_vide( stream_t *p_stream, MP4_Box_t *p_box )
     MP4_GET4BYTES( p_box->data.p_sample_vide->i_qt_data_size );
     MP4_GET2BYTES( p_box->data.p_sample_vide->i_qt_frame_count );
 
+    if ( i_read < 32 )
+        MP4_READBOX_EXIT( 0 );
     memcpy( &p_box->data.p_sample_vide->i_compressorname, p_peek, 32 );
     p_peek += 32; i_read -= 32;