Memory leak on decoding a malformed image

[Shnatsel]

lodepng-rust leaks memory when given malicious input. This issue has been discovered via fuzzing with afl and libdiffuzz, later confirmed with address sanitizer.

Steps to reproduce:

1. Download and unpack lodepng-repr-diff.tar.gz - this is a Rust project with Cargo
2. cd lodepng-repr-diff
3. cargo build --release
4. run target/release/target/release/lodepng-afl-fuzz-differential < memory_leaking_files/id:000000,sig:06,src:000389,op:havoc,rep:2 and observe memory consumption of the process steadily increase. This should be the case for any file from memory_leaking_files/

This issue has been discovered in version 2.3.0, so it is distinct from #28

[kornelski]

I've tried these files with valgrind --leak-check=full and it didn't find any problems in 9a72cc4.

I believe that is the same issue as #28, fixed in 37a7bcc. That commit wasn't part of 2.3.0. I've corrected that by releasing 2.4.0.

Thank you for fuzzing the codebase. I appreciate it. 2.4.0 has migrated from a custom vector type to Vec, so it could have new bugs :)

[Shnatsel]

Closing as duplicate of #28