Description:
------------
According to `man realloc`, realloc() may return NULL if a valid pointer and size=0 is passed, e. g. realloc(<ptr>, 0) is the same as free(<ptr>). However, __zend_realloc always interprets NULL as OOM and therefore bails out when trying to reallocate a pointer to size 0. For example, mysqlnd sometimes calls erealloc(<ptr>, 0), which will crash PHP when running with USE_ZEND_ALLOC=0.

From zend_alloc.c, lines 2834 - 2841:
ZEND_API void * __zend_realloc(void *p, size_t len)
{
	p = realloc(p, len);
	if (EXPECTED(p)) {
		return p;
	}
	zend_out_of_memory();
}

It should probably be something like if (EXPECTED(p) || !len).