happy crashing in [OwlShmBuffer invalidate]

[RJVB]

I'm getting regular crashes under [OwlShmBuffer invalidate], most often with this backtrace:

0   libwayland-server.0.dylib     	0x000000010ac92f06 wl_shm_buffer_get_data + 20 (wayland-shm.c:459)
1   io.github.bugaevc.Owl         	0x000000010ac4903c -[OwlShmBuffer invalidate] + 108 (OwlShmBuffer.m:64)
2   libffi.8.dylib                	0x000000010accb052 ffi_call_unix64 + 82
3   libffi.8.dylib                	0x000000010accfba7 ffi_call_int.llvm.BC09A206 + 807
4   libwayland-server.0.dylib     	0x000000010ac9633d wl_closure_invoke + 382 (connection.c:1035)
5   libwayland-server.0.dylib     	0x000000010ac8fb87 wl_client_connection_data + 990 (wayland-server.c:438)
6   libwayland-server.0.dylib     	0x000000010ac93540 wl_event_source_fd_dispatch + 132 (event-loop.c:135)
7   libwayland-server.0.dylib     	0x000000010ac93bc4 wl_event_loop_dispatch + 204 (event-loop.c:1064)
8   io.github.bugaevc.Owl         	0x000000010ac4edb1 socketCallback + 17 (OwlRunLoopSource.m:49)

This is because the _buffer pointer is corrupt, but I haven't yet been able to find out what causes that, or where. The issue doesn't occur when I run Owl under valgrind.

Best I've seen is this:

Mar  8 23:53:28 Portia.local Owl[91231] <Error>: CGImageCreate: invalid image size: 255 x 0.
Mar  8 23:53:28 Portia.local Owl[91231] <Error>: CGImageCreate: invalid image size: 255 x 0.
Buffer address requested when its parent pool has an external reference and a deferred resize pending.
2025-03-08 23:53:39.815 Owl[91231:d07] Unknown shm format

(in that case the crash occurred in wl_shm_buffer_begin_access(), wayland-shm.c:637 ; the CGImageCreate warnings occur only when running with jemalloc.)