Image Magick has a Memory Leak in coders/ashlar.c

Memory leak exists in coders/ashlar.c. The WriteASHLARImage allocates a structure. However, when an exception is thrown, the allocated memory is not properly released, resulting in a potential memory leak.

```bash
==78968== Memcheck, a memory error detector
==78968== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==78968== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==78968== 
==78968== HEAP SUMMARY:
==78968==     in use at exit: 17,232 bytes in 4 blocks
==78968==   total heap usage: 4,781 allocs, 4,777 frees, 785,472 bytes allocated