GHSA-5vx3-wx4q-6cj8

## Summary

NULL pointer dereference in MSL (Magick Scripting Language) parser when processing `<comment>` tag before any image is loaded.

## Version

- ImageMagick 7.x (tested on current main branch) - Commit: HEAD

## Steps to Reproduce

### Method 1: Using ImageMagick directly

```bash magick MSL:poc.msl out.png ```

### Method 2: Using OSS-Fuzz reproduce

```bash python3 infra/helper.py build_fuzzers imagemagick python3 infra/helper.py reproduce imagemagick msl_fuzzer poc.msl ```

Or run the fuzzer directly: ```bash ./msl_fuzzer poc.msl ```

## Expected Behavior

ImageMagick should handle the malformed MSL gracefully and return an error message.

## Actual Behavior

``` convert: MagickCore/property.c:297: MagickBooleanType DeleteImageProperty(Image *, const char *): Assertion `image != (Image *) NULL' failed. Aborted ```

## Root Cause Analysis

In `coders/msl.c:7091`, `MSLEndElement()` calls `DeleteImageProperty()` on `msl_info->image[n]` when handling the `</comment>` end tag without checking if the image is NULL:

```c if (LocaleCompare((const char *) tag,"comment") == 0 ) { (void) DeleteImageProperty(msl_info->image[n],"comment"); // No NULL check ... } ```

When `<comment>` appears before any `<read>` operation, `msl_info->image[n]` is NULL, causing the assertion failure in `DeleteImageProperty()` at `property.c:297`.

## Impact

- **DoS**: Crash via assertion failure (debug builds) or NULL pointer dereference (release builds) - **Affected**: Any application using ImageMagick to process user-supplied MSL files

## Fuzzer

This issue was discovered using a custom MSL fuzzer:

```cpp #include <cstdint> #include <Magick++/Blob.h> #include <Magick++/Image.h> #include "utils.cc"

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { if (IsInvalidSize(Size)) return(0); try { const Magick::Blob blob(Data, Size); Magick::Image image; image.magick("MSL"); image.fileName("MSL:"); image.read(blob); } catch (Magick::Exception) { } return(0); } ```

This issue was found by Team FuzzingBrain @ Texas A&M University