Travis Cross 3c32dd3bc9 Return NULL from sub_alloc for zero size
When zero was passed for the size to `sub_alloc`, we were passing this
size on to `malloc` or `calloc`, which is unusual enough that static
analyzers warn about this (POSIX says that either NULL or a pointer
will be returned).

We'll instead just return NULL right away.
2014-08-22 02:47:04 +00:00
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