This must be "return MemoryContextAllocationFailure(context, size, flags)"
instead. The effect of this oversight is that if we got a malloc
failure right here, the code would act as though MCXT_ALLOC_NO_OOM
had been specified, whether it was or not. That would likely lead
to a null-pointer-dereference crash at the unsuspecting call site.
Noted while messing with a patch to improve our Valgrind leak
detection support. Back-patch to v17 where this code came in.
a05cf22e05