add malloc failure test for cgif_raw API

[dloebl]

Iteratively fail each malloc call in the cgif_raw code path (newgif + addframe + close) to verify all allocation failures are handled correctly without crashes.

[dloebl]

Found by the new ealloc_raw test with ASAN:
When an early malloc fails, the goto cleanup path frees all pContext fields, including ones never assigned. Zero-initialize pContext so unassigned pointers are NULL and safe to free.

[Copilot]

Pull request overview

Adds a targeted regression test that injects malloc failures across the cgif_raw encode path to ensure allocation failures are handled cleanly (no crashes / invalid frees), and tightens internal initialization to make failure cleanup safe.

Changes:

• Add a new Meson test target (ealloc_raw) that compiles cgif_raw.c directly so malloc can be intercepted.
• Introduce tests/ealloc_raw.c, which iteratively fails each malloc call during cgif_raw_newgif + cgif_raw_addframe + cgif_raw_close.
• Zero-initialize LZWGenState after allocation to ensure cleanup paths can safely free() partially-initialized members.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/meson.build	Registers the new ealloc_raw malloc-failure injection test executable.
tests/ealloc_raw.c	Implements iterative malloc failure injection by compiling cgif_raw.c into the test TU with a malloc macro override.
src/cgif_raw.c	Initializes LZWGenState to zero to make allocation-failure cleanup safe.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[MCLoebl]

Looks good. Minor stuff: is the initialization in l.11,12 of ealloc_raw.c needed? I suggest replacing n by the more intuitive name fail_after in l.69, 78, 87 as well.