Use of uninitialised value in function DtsCheckSync()

Previous title: Segmentation fault in function DtsCheckSync()

Describe the bug

We found a SEGV caused by a use-of-uninitialised-value bug in function DtsCheckSync() after testing one of the harnesses provided on the OSS-Fuzz repository (vlc-demux-dec-libfuzzer).

To Reproduce

In the attached archive you will find:

• the executable on which we performed our tests
• the input file that caused the bug
• the output of Valgrind as additional info

To reproduce the errors, simply run the given binary with the testcase files with a command like ./vlc-demux-dec-libfuzzer /path_to_testcases/input

The program has been tested on the standard Docker image provided on OSS-Fuzz using Ubuntu 20.04, providing AFL++ as fuzzing engine and build flag --sanitizer=none.

The hash commit used to perform the tests is fb18df8.

Environment

• OS: Linux
• Version/Distribution: Ubuntu 20.04
• Architecture: x86_64